Crates/Supply Crates are a type of power-up that appear in SAS: Zombie Assault 3 and SAS Zombie Assault Tower Defense. They are white/tan boxes with a red silhouette of a M16A4 on top of it. Simply walking over them (in Zombie Assault 3) or clicking on them (in Tower Defense) picks them up.
Once the player unlocks the Radar Scanner skill in Zombie Assault 3, they can spot Crates on the minimap as blinking yellow dots.
Crates can give the player various things, including Grenades, Cryo Grenades, Holy Hand Grenades, Cash, Guns, Sentry guns, or Experience Points (although they don't give XP in the mobile versions of SAS 3). All power-up guns only have a limited amount of ammo and once used, will disappear. Additionally, in some Daily Missions in SAS 3, they serve as First Aid Kits.
Power-up guns greatly help especially at low levels, where there are very little to no powerful weapons available. Crates will not always spawn when needed; once a crate is collected another one will not spawn until a certain amount of time has passed.
In Zombie Assault Tower Defense, crates are periodically air dropped, and can contain cash, grenades, or premium air support.