DS (6) is going away camping with Beavers for the first time in a couple of weeks. Only one night initially, then two nights later in the summer. I cannot figure out what kind or size of rucksack to buy, he only needs clothes and sleeping bag, rain gear etc. I want it to do him when they go away for longer periods, but I don't want it to be much too big now. I did order one online but it's much too small. Anyone any ideas or recommendations. TIA eos