The new brushless Summit will probably be good. Mini E-revo size, with bigger wheels and some minor upgrades.
http://www.amainhobbies.com/product_...y-Wall-Charger
Check out the youtube vids. It handles offroad terrain extremely well.
Either that, or you could buy a 1:10 or 1:8 sized monster, like the Flux, Summit, AX10 crawler, etc, and take off the wheels and just screw them back on when you've arrived. I think that will easily fit in a backpack, and it just takes a minute to screw the wheels back on.