pantsOne pair of jogging pants, which can be put on in the train, used at night or used as long underwear, one pair of long pants (as rugged as possible) and two shorts (it is useful if one of them can be used as swimming trunks, of course this only works for the guys).
jacket
You don't really need a big, warm jacket. Just put on all your clothes, sweaters, shirts and so on and take a train to a region with more sun.
rain protection
It is best to take off everything except your underwear or to wear a swim-suit or swimming trunks and to go on like that. Alternatively of course, you can wear a raincoat. Usually, when it's raining and the weather is bad, you'll take the next train and go to some other place where the weather is better. That's the great thing about InterRail.
shirts and pullovers
Three t-shirts and two pullovers (a thick one and a thin one) are usually enough. If you wear them on top of each other they can also serve as a jacket.
underwear
Three underpants or boxers are usually enough. (this amount can be reduced if you wear those boxershort similar trunks with the net inside)
clothes for going out
I always have a shirt and trousers with me. It's nice to have some good clothes for a date or so. But usually they won't stay "going out clothes" for very long (that would be a bit foolish), because at one point you will wear them anyway. "Going out clothes" doesn't mean you have to keep them in a vacuum-sealed plastic bag so they stay clean! On the other hand, it's never bad to have something special with you, just in case.
washing dirty clothes
You can either take a small bag of washing powder along with you or use your shampoo. Shampoo is pretty good to wash clothes with, because it also dissolves in saltwater. And if you really need it, you can always find small amounts of washing powder in the supermarkets in the train stations.
sandals
I found the ones from "Teva" quite good. But I have to admit, I haven't tried any other brands so far. You should be able to walk comfortably with your sandals for a couple of kilometers and the sole has to have a good grip, then you can also walk through water without slipping. However, the insoles of sandals often aren't as good as the insoles of hiking boots. It might be that, after wearing sandals non-stop for a month, the back of your feet start hurting. Otherwise sandals are great for showering in dirty showers or as slippers.
socks
Three pairs of socks should be enough because you don't wear socks in sandals anyway. In hiking boots it is better to wear socks, as otherwise they will turn black inside due to the sweat. Special padded hiking socks are very comfortable, but they aren't so cheap (10 to 15 EURO for a pair) and in the summer season they are usually too warm, even the ones made especially for summer. My brand: "Thorlo" socks for about 8 EURO.
shoes
One pair of (light) hiking boots or something similar. You have to spend around 150 EURO for good hiking boots, but therefore it will be a pleasure for your feet. You can get a leather insole and you will also need some padded hiking socks. Important: if you buy hiking boots, take your time and go to a good store. The shoes should be tried on with thick hiking socks (there are always some lying around in good stores). Try different shoes and walk around with them. It is very important that the shoes fit well. They'll probably still pinch a little when you try them on for the first time, but there shouldn't be any points of extreme pressure. Before you start your InterRail trip you should have worn your shoes for at least two weeks, otherwise you will get blisters. Hiking boots can also be bought with "GoreTex" equipment. In average, they cost about 25 EURO more and they are waterproof. I've had my leatherboots for three years now and so far I have always been totally satisfied with them. My brand: "Handwag Yokon" for 150 EURO.
Food:
food
This depends on how much you can carry. I always have three bags of instant meals with me in the bottom of my backpack just in case. (They cost about 3 EURO each. Put them in boiling water, or in cold water, and let them draw for about 10 minutes). Most of the time I eat them anyway, because often I'm too lazy to look for a supermarket. Otherwise noodles with sauce are the easiest and cheapest method to fight hunger. Canned food and food in general (I find) is quite expensive in Scandivia. To prevent scurvy (some have already died from it ....*joke*), you should eat some fruit from time to time.
fluids
I always have two 1.5 litre plastic bottles in my backpack. If they get too dirty I can always exchange them for new ones.
dish-washing
I always use shampoo for doing the washing, you can use it for everthing and it also dissolves in saltwater. You can also just use water by itself.
dishes
Besides two little pots and a lid which also serves as a plate, I always have a high grade steel cup with me (I couldn't do without my (hot) chocolate in the mornings). It also tastes better! Of course you shouldn't forget camping flatware (a fork, knife and spoon) and a pocket knife to open cans and bottles etc.
stove
Actually a camping-gas cooker should do. (you can save a lot of money by cooking yourself). The only bad thing is that if the gas canister is empty it is hard to find a replacement. But that's life. To avoid such situations you can get a gasoline cooker. But for 75 EURO they are more expensive than gas cookers.
accessories
Without these little helpers the most beautiful meal doesn't taste good: a pocket knife with a corkscrew and a can-opener, a seasoning-mill or salt and pepper in little containers and small plastic boxes are perfect for cheese or sausages.
Sleeping:
sleeping bag
You should be aware that you might use your sleeping bag for 30 days or so and that you will spend about a third of every day sleeping in it (or at least trying to sleep). Different criteria determine the choice. The material: I would buy a sleeping bag with a synthetic fibre filling. It weighs more than a sleeping bag with down feathers, but if it ever gets wet, it will dry a lot quicker. The synthetic fibre sleeping bag doesn't attract moisture so much and therefore it stays warm even if it gets wet (because drying isn't always possible during a trip). The packing volume of a synthetic fibre sleeping bag is higher than that of a down feather sleeping bag, so be careful that it isn't too big (10 liters packing volume is about the limit in my opinion). Another advantage is that synthetic fibre sleeping bags are less expensive and you won't feel the difference in filling material anyway. A down feather sleeping bag has the advantage that it is smaller to pack, lighter and also warmer than a synthetic fibre sleeping bag.
how to take care of your sleeping bag
Clean your sleeping bag only with a fine detergent. You can find them in special outdoor stores. They cost about 5 EURO each and one is enough to clean your sleeping bag three times. But you shouldn't wash it too often. It isn't good for the filling. I clean my sleeping bag once or twice a year, depending on how much I use it. You can also just open your sleeping bag and put it out into the fresh air. Never use a laundry-dryer to dry your sleeping bag.
sleeping bag size
When you buy a sleeping bag, pay attention to the size. I bought my first "Ajungilak Igloo" with a length of 195cm, even though I'm only 178cm tall. The shop assistant (it was in an outdoor-sports store in Oslo) told me that the 180cm sleeping bag was for women and the 195cm one was for men. In the end I found out that my sleeping bag was much too long for me. I always had cold feet in it. Luckily my brother is very tall, so at least he can use the sleeping bag now. So, never buy a sleeping bag that is too big. Another important thing is to try your sleeping bag before you buy it. It might be that the 180cm sleeping bag is too small for somebody who is 178cm tall but has wide shoulders. But I guess the companies had something in mind when they made the sizes.
mattresses
There are self-inflating mattresses and the well known foam mattresses. I use a self-inflating mattress because it is more comfortable. But it is always a matter of price. There are simple foam mattresses from 5 EURO to 20 EURO and self-inflating mattresses from 35 EURO to well over 100 EURO. My self-inflating mattress (from "Therm-a-Rest", but there are also a lot of other good manufacturers) cost 60 EURO and I am very happy with it. It is very small to pack (30 x 15cm) and fits into my backpack. The weight is about 650gram.
tent
I had the experience that a tent for 30 EURO can turn into a swimming pool or a water reservoir. After a rain shower there is more water inside than outside of the tent sometimes. So either you sleep in a hostel when it rains and somewhere outdoors when the sun is shining or you buy a good tent. For a good tent you usually have to pay over 150 EURO. But I have to say, also a cheap tent can survive an InterRail trip. A cheap tent normally weighs more and in heavy winds a tent pole may break. A more expensive tent for two people weighs around 3kg. My tent is from "Salewa", but there are a lot of other manufacturers aswell. "Tatonka" tents are also cheap and good quality.
Washing:
soap etc.
If you do not have too sensitive skin, shampoo is the best because it is also useable as soap in saltwater. Besides, if you have two big packets (one for shampoo and one for shower-gel) in your backpack, it will weigh too much. Furthermore you will only need about half of the packets, as you probably won't have the opportunity to wash so often.
towels
Travel towels (out of felt similar material) are the best. They are small, easy to pack and dry fast. They cost about 2 EURO each. Normal towels and bath towels use too much space and are heavier.
small things
Toothbrush, toothpaste, sun-cream (also serves as normal skin cream), shaving equipment and nail clippers or scissors which you can also use for other things.
Others:
photography
I always have a pocket camera with me. They are light, small and do not need a lot of space and if you lose it, it isn't so expensive to replace. I have a bigger camera now. The photos are a lot better in quality, but the camera needs a lot of space and I always have to be careful that it doesn't get stolen. If you have enough money buy a digital camera. They are simple to use and very comfortable. Don't forget to take a big memory card for the photos, because it won't always be possible to download the photos from your camera and to e-mail them home.
discman, mp3-player
A nice gadget to relax on long trips. If you are sitting in a train for 10 hours, the others in your compartment might be annoying, so an mp3-player is perfect. If you can receive radio, you can always listen to the music stations in foreign cities.
your own pharmacy
I always have one packet of coal pills with me against diarrhea, one tin of multi-vitamin pills, one packet of aspirin and plasters for blisters. You can manage quite well with that. They speak English in most pharmacies, in case you need some special medicine.
books
If you are bored of looking out of the window at the landscape, it is nice to have something to read. You can also exchange the books with other travellers.
pocket knife
A pocket knife is not only useful for the kitchen but also to repair the backpack and so on.
Source http://www.interrail.net