Some nice but reasonable suggestions:
Scrap cars that can be used for cover
Large buildings (at least 1 big building that can have several people inside defending while the rest of the players attack it)
trenches? cool although may be a hazard if someone falls in accidently, or if theres a lot of rainfall
mini "town" (just a bunch of small buildings where small games can be played, usually pistol's only as you get up close and personal)
Sniper tower (the higher the better, even better if it had a lockable trapdoor from the inside)
"Safe zone" right in the middle of the field where players can go to clean out fogged goggles/use bathroom/grab some water
"I feel no emotion, just recoil."