If your vehicle has a 6 volt system it's an old vehicle. If it's an oldie, is it a manual tranny? If it is, head it downhill and at about 6 mph pop the clutch (or get some friends to push it, assuming you have any friends) and the engine should start. Once it starts, don't stop it until the battery's charged.

If you have friends and they're pushing, you can help them a lot by having the car in neutral and the parking brake off. If you get a push from another vehicle AND the other guy's airbags don't go off be certain there's a gap of about 10 or 12 feet before you pop the clutch or Bad Things will happen to the pusher.