I use plaster molded rocks sold at hobby stores, real rocks, aquarium rocks, reptile bark, static grass, flock, sand in various grits, plasticard in various styles (you can buy it plain or with grooves and tiles pre-engraved), metal modeling mesh (sold at hobby stores), Woodland Scenics Water Effects, brass rod, guitar strings (usually I use these for actual model conversions), 2 part epoxy mixed with inks (for making standing pools and puddles). And of course various bitz for bodies etc.