Along with a more usual list of things to bring (toothbrush, first aid kit, etc.), I realised along my travels that they were certain things that were handy to have, that nobody ever recommended to me.
- Rucksack which opens like a suitcase - nice big padded shoulder straps (preferably that leave room for your back to breathe), and waist and chest straps. If you get a more traditional top-opening rucksack, be prepared for frustrating 'why is X always at the bottom of my bag?' moments.
- Small combo padlock(s). Use them on your rucksack (though dedicated thieves can rip through the fabric). Some hostels just have lockers, with either no locks, or a fee to use their locks. Bring your own, and try get combination locks so you don't have to worry about keys. Always reset to zero, and you'll be able to open them in the dark (with practice), or tell when someone's been trying to get at your stuff.
- Pocket torch for entering dorm rooms at night. Or use your phone light.
- World Traveller ATM card - I didn't have one of these. Apparently a lot of banks do a debit card that has little/no fees for international withdrawals/conversions. Talk to your bank to see if they do something. Consider switching if they don't.
- Decent daybag/small rucksack - the ones that attach to a big rucksack can be useless. I never attached mine in six months of travelling.
- Unlocked mobile phone - make sure it's unlocked before you go. O2 took a month to unlock mine. Then in any country, get a local SIM card and be more independent. If you've a smartphone, you can use it for data too, save you internet café charges.
- Bring a student card. Even an out of date one can be useful for discounts in non-English speaking countries, especially if you're polite. Helps if it's not in English - Irish, for example.
- First Aid Kit - see Gadling for more
- Travel adaptor with USB - saves you having to find a PC to charge your iPod or whatever.
