In the story mode. There is a boss that constantly shoots. During this time, it is necessary to run around in order to beat this boss. This is also effective in multi player.
In the mission with the ladies shower room, go into the locker room and open up the lighter gray lockers, one has a host collectible, another has a gamecube in it, and the last one has Samus Aran's helmet in it.
Throughout single player mode, you'll find ghost and host collectibles, ghost collectibles look like green stuffed animals, and the host collectibles look like two letter V's on each other. The host collectible unlocks new options for the multiplayer mode, and the ghost collectible gives you more life.
Make sure to be gathering at least some of the collectibles because when you're going up against the Last Boss, he'll easily take you out quick. Then you'll have to go back through all of the levels looking for collectibles and that's a pain the butt...
when you are Mr.Volks and you run out aff ammo go to the ammo box a tap "A" a bunch of time insed of 1 and every time u shoot your ammo goes back up to normal TADA <img src="http://i.neoseeker.com/d/icons/smile.gif" border=0 vspace=2 alt="" />
When you first hit the morgue, run into the area with the refrigerator open it get the collectible and then restart that level and go back it'll still be there. You minus well run straight through the fire also.