I really recommend your buddy wait on the expenditures until he has researched it himself a bit more. While there is an almost inexhaustible list of suggestions for gear we could come up with here, I think by far the best he can do is to get out there and try what he's got now or what he can get for little or nothing and see what his needs might be. Gearing up really needs to be secondary to thnking through. Perhaps a better investment of the $600 would be more education/instruction and hands on time.

I think you've got him set up well enough as is for now. Let him do some discovery first, then maybe he will come up with a specific list of needs/desires that we can help him with that will be a lot more meaningful.

For a quick, general recommendation now, I'd say if he's in the wilderness he will need shelter, a way to acquire and purify water, a means of making fire, and a means of signalling both visual and audible. With the right training, all of these can be met real cheaply, like less than $100 for sure.