That's why I always, always, always carry one of these, especially when I'm out on my own
that's not the one i have, but close. I've lost count how many times I've had to use it, not only for myself, but for other people on the road. Much more convienent than jumper cables (if you can even find another car around to get a jump from), and there are some situations when jumper cables just aren't possible to use. Plus, couple it with an inverter and you have AC power wherever you go. I've had complete strangers offer to buy it from me after I jumpstarted their cars for them, I guess they've never seen one.
My original one was still going strong after 4 years, but I decided to trade it in for a smaller model. Much lighter and smaller, and a lot cheaper. The one I have now weighs about 7 lbs and is smaller than a shoebox. These are NOT the same as those glove compartment units, where you have to plug it in to the cigarette lighter and let it recharge a weak battery. This has to be connected directly to the battery and will start a completely dead battery. So now I never have to worry about leaving my lights on or radio on when I'm camping in the car, cuz I know I can just jumpstart it in the morning.