One thing I didn't see anyone mention, but would SURE be on my list of things would be to take along a pair of mountain bikes. See how many species you can identify. Take binoculars or a telecope and a star guide up for evening stargazing. We never go out without planning on rock climbing. Rafting or canoing.
Nature photography is fun.
Well, that is really my thing. H ever got into it. Build something together for use in the outback. Perhaps a kit for a barbecue, a kite, or a rowboat. Take simple acoustical instruments, like harmonicas, recorders, or guitars.