As the others have said, the most useful knife for him would be a Victorinox of some sort. Mine was made by Camillus a long time ago, but it was the same idea. We were allowed to use fixed blades in the Boy Scouts above Tenderfoot. Here, practicality is, again, the rule. Something like an Kershaw Field Knife, or even the Mora that was mentioned. It should not be large. I had a Buck and they are hard to beat. 4" is about right with 3 1/2 on the short side.