Crowbar
A metal bar with curves at both ends for prying.

It's a useful took for pulling out nails, breaking open doors, tearing holes, breaking things, and just about everything else you can do with a metal stick.

It also serves as a nice weapon, the bar is heavier than a baseball bat and the prying ends can create some wounds that a knife can't.
Hey! I need a crowbar to open this door.
Half-Life's most useful weapon is the crowbar.
Some dumbass broke into my house with a crowbar and tried to use it on me before I shot him.