I found the rocks near a creek that runs behind my house. Just made sure they weren't limestone based, then washed them up well before I put them in my tank. I like the natural look in aquariums but am leary of driftwood since I've had some bad experiences with them leaching tannins profusely.
Most plants will work in sand; in fact some like Hairgrass actually needs a finer substrate to spread well. You may have to use root tabs if you have plants that are heavy root feeders, but you would have to do that with a gravel substrate as well.