Red Faction Guerrilla

There are ten backpacks in the game:

Heal
Tremor
Fleetfoot
Jetpack
Concussion
Rhino
Thrust
Stealth
Vision
Firepower

Most maps have 5-7 different backpack stations, but you can also edit players' starting backpacks in custom matches.

Note that you don't need to kill anyone with the backpack's ability or have it be active. As long as you're wearing the backpack, any kill credited to you will count. (Though needless to say, kills with the jetpack in the campaign don't count.)

You can track your progress in this achievement through the Backpacks tab of the multiplayer stats page.