The Bosch Pocket Saw is a simple, cheap portable unit that accepts standard T-shank or reciprocating saw blades—like those that go into the nigh-on-magical Milwaukee Sawzall—when you just need to chew through something without pulling out the power tools. The Pocket Saw comes with a couple of blades, one multi-purpose and one for wood or drywall, and can store more blades in the handle. You can even kick the handle down to a 60° angle to get a little more oomph into your cuts. Not too shabby at all for fifteen bucks.
An Inexpensive -- But Useful -- Pocket Hand Saw [ToolMonger]