Ditto what other people have suggested for modeling terrain. For vegetation, take a walk around campus and see what kind of dried vegetation is around (fuzzy grass seed heads, yarrow, juniper, etc). Arts & crafts stores are great places to hit up as well for wood, dried vegetation, chip board, foam core, just walk around and think about the scale, form and textures that you want to represent. Most of all, have fun, use your imagination, try different textures, colors and see what works for you!