You're not allowed to use mods that in any way provide an advantage over another player or that change the way the game works. Some examples are -
ELM (unless you're in sasp/fbi/saes etc)
Most all cleo mods
Skin mods that change the size of your character to anything smaller
Car mods that change your car to anything smaller
the previous two are mods I've seen people get banned for healthacking with, cause it changes the "hitboxes", where you take dmg, on your character.
basically, just use common sense. if you find a mod that you think is non rp, it most likely is