My favorite idea is the map. With everything being digitalized its possible to customize a map. What if you customized a map of a place you planned on hiking with kid friendly symbols. Maybe symbols for campsites and bridges and a few imbedded pictures printed on the actual map.
It might take some work and I'm not sure which program too use but I think the result would be cool. Your little guy could look at his map and know where he was and where he was going. When you cross a bridge or a creek he could find it on the map.
-Maybe a cheap digital camera? Don't know if that is too complicated or not.
-Animal track identification cards. Don't just tell him 'Those are deer tracks, have him find it on the cards for himself. One thought, make sure the card or sheet has pictures since 5 year olds don't read much. You could actually make this yourself. Take pictures off the net put them on a sheet and have it printed and laminated.
-A bright whistle might be cool, teach him to blow it if he gets lost.
-A cheap hammock, chances are he won't sleep in it but it might be a fun novelty, that is why I'd emphasize cheap.
-A survival book with lots of colorful pictures (make sure there is nothing disturbing in it though). He can look at pictures of lean-to shelters or wooden fish hooks and have fun making his own version in the back yard.
-Boys love fire. If you think he's old enough you might give him an outdoor lighter and let him start lighting fires (with supervision of course). I'd suggest one of the bigger fancier ones that will put out more heat so he'd be more successful.