When low on health and there are no health pick-ups, use friendly-fire to kill the player. Then, revive him. Reviving a player restores him to their full health, and may be something to consider on the Inferno difficulty.
Unlock one of the following Pesticide guns as a reward for reaching Rank 8 with any of the four corresponding Armor classes. Note: Reaching Rank 8 is only possible under the Inferno difficulty setting:
When taking a weapons box (or salvage box) during an online match, all players in the match get the weapon (press TRIANGLE or Y at the end to see salvaged weapons) regardless of who picks up the box. However, the notification of what you get doesn't appear on your screen.