I've been tasked with buying some presents for a departing colleague whose about to go round Europe inter railing. She's traveling for a month and then going back to Australia. I did think about those micro fibre towels.
Swiss army knife although with the obvious rider that she shouldn't carry it in her handluggage going through airports. Or one of those locks that you can chain your backpack to stop robdogs people from pinching it.
The thing about backpacking (I spent years backpacking in my pre-children days) is that you don't want ANYTHING extra. not binoculars, not anything. Well meaning people gave us things like that which we had to leave behind. Unless you ask specifically for something she hasn't already got.
And any money left over, you could put on a cash passport so that she has some extra money for fripperies as she travels round. To make it a bit more personal, you could write in a card your suggestions for what to do with it - sachertorte in Vienna etc
Thanks for the suggestions - I got her the microfiber towel, some earplugs for any hostels, a washing line, a small torch and I took on board what people said about traveling light and we bought euros for her.