Many years ago we got a car emergency kit as a gift. On the whole the piece that we've used most has been the air compressor.
It isn't that there aren't a lot of good tools in the kit. It has a rather nice emergency triangle, but it has been the air compressor that has saved the day most often.
It's snowed a lot the past few weeks and I haven't checked the tire pressure since it got cold. But today at the store when I was adding windshield washer fluid I noticed one of the tires was pretty low. It was down to half pressure. I guess I shouldn't be surprised there are a lot of pot holes and they are very good at knocking air out of a tire. So I pulled it out, pulled it into the cigarette lighter and let it do its thing. It took only a few minutes and we were back at full pressure.