Step 8: Squeeze the last juice from a car battery
Pry off the cover of the battery with a screwdriver or pry bar and drop two crushed aspirin into each cell of the battery. Theoretically, this should cause a chemical reaction that changes some of the sulfuric acid into acetic acid and provide just enough oomph to get the engine to start turning over.
For bonus MacGyver points, try using cola to take any corrosion off of the terminals. If it's really cold outside, heat up the battery with whatever you've got on hand. Pouring hot water over the engine and battery itself (with everything disconnected) might help. YMMV. Literally.