I don't have one but here's a good link:
Tire Inflator Comparison
Could be very handy to have.
I now have an 8 gallon compressor at home (it is too big to carry with me) because one evening after work we were heading to a campground about 2hrs away. I had 76 & 75 in the rear tires and wanted to get them up to 80. The first gas station air pump was blocked by someone who just started vacuuming his car so I decided to go to another station a couple of miles up the road. That one was really busy with three cars parked in front of the pump so I pushed on. At the third station the pump let the air out of my tire so I was down to 70 psi. At the fourth gas station I waited for a truck to gas up and pay so I could get access to air only to find that the pump was out of order. Finally, at the fifth gas station, I got air!