Health pickups would be nice. I'd remove the 20x ammo thing, weapons should be a choice and frequently swapped or thrown away. (Perhaps reduce the power of e.g. the M4, Uzis, Rayguns so they aren't just the absolute best weapons)
Recolourable player model
Setskinname. Put some more textures in base/data/shapes and use %player.setSkinName("team1") or something. (Replace ".blank" with ".team1") doesn't seem to work
Hats vs No Hats? Or copy Guy.dts + textures to a new folder and change them.
Also, player.setCloaked(1) works to make them mostly invisible on a dark background

(enemies still see you)