Halo 1 featured powerups, such as overshields and active camoflauge (invisibility).

Currently there are no powerups in the game, although they might be added later. (Editor's note: this gets a big thumbs-up from me. I've never ever bothered to cycle powerups like the active camo or the overshield, and never thought I should be punished for wanting to get right on with playing instead of going shopping.)