Well, having been there, done it and got the odd t-shirt along the way, I can say Well Done for choosing this sort of thing to get him, as the cost doesn't half mount up. Good ideas may include...: Lonely Planet guides (although not too many - they ARE heavy!), mosquito net (believe me, he will thank you for this), travel towels (light, easy-dry - they DO begin to smell after a while though - or was that just me?), Swiss Army Knife (always comes in handy), travel washbag (dead handy, they fold out and hang up), even some good novels to read while he's away, although bear in mind that space in one's rucksack is always a priority / concern. I would avoid buying clothes, such as shorts / t-shirts as he can easily pick them up on the cheap in Thailand / Bali / wherever. A rucksack, although a great present given its cost is really something that he needs to choose as they HAVE to be comfortable - this is something which he will be living out of and carrying everywhere for the next 12 months and take it from me, if it's not comfy, it will become a pain the proverbial. Good luck!