Back in the day I always carried a fairly well equipped hip-box, two bottle jacks and a couple 6" pieces of 2x4. One bottle jack might fail, unlikely both. A rule my father drilled into my thick head, never get under a vehicle without something thicker than you are. In the old days, a spare tire was good, today I doubt I could get the car high enough so I just carry an iPhone and a gold Visa card. 
