Approach a Powerade vending machine and press [Action] near the buttons on the machine. A Powerade will pop out.

In the Nuclear Plant level where you get the UMP, look at the wall just before you go up to the tower to find a Powerade vending machine.

If you have low health and are in trouble, go to a Powerade machine. Press [Action] and a Powerade will pop out of the machine. Run on top of it, and if done correctly it will fill up your health.