"Wasteland": Easy kills
Go to Wasteland on a online multi-player game with a Sniper class set up. The Pavelow, an air strike of any kind, and sentry gun is recommended, along with the thermal scope and tac. insertions. Go to the area where the house is next to the graveyard. Do not go in the house. On the opposite side of the house away from the graveyard is a white wall with a mounted machine gun. Crouch behind the wall and move around until you can just barely see over it. Watch the area around the house. Enemies will frequently run by. Pick them off as they do. You can get enough kills for kill streaks, then let them do the rest.