Backpack sized off-roader?

You can always get a backpack designed for skateboarding, they have a big strap on the back to hold skateboards, maybe you could use it to hold water car you want and but the rest of the stuff inside the bag? As for an actual RC, if I was in your position I'd get a 4x4 Stampede, Hyper 10 Truggy, or an 1/8 buggy.