It's funny to hear about what people want to carry around and I look back at those things I would not leave home without. Good Jumper cables, air gauge, 12V air compressor, and a light for emergencies. Then I got concerned about my own 12V battery system and concerns about jump starting someone else.

While I was shopping at Sams Club for another 12V air compressor (mine burned up), I saw this Jump-Start system called Power On Board for ~$49.
I bought it and found it to be very useful. It has a strong built in air compressor with a nice gauge. I don't have to run a 12V power supply to my vehicle lighter plug any more. Heavy duty short battery cables so you can jump start with 450 amps most 12V systems without parking like most cars having to use those long cables. It powers and recharges DC electronics and has a USB charging port.

It's so much easier and quicker to fill the tires on all my cars and lawn equipment and doesn't take up much more room than the old air compressor with that long cord. In addition, I can take it with me in my boat for needed power supplies like cell phones and jump starts.

Here is a list of what its got:
Item: 413503
Model #VEC012P0B
12 volt DC output socket with automatic short circuit protection

Features

12 volt DC portable power supply
260 PSI air compressor inflator
450 amp instant starting power
Built-in emergency area light
Charging and battery status indicators
12 volt DC output socket with automatic short circuit protection
26 inch heavy-duty welders type cables
Rugged, weather-proof, unbreakable housing
Automatic charger prevents over-charging during AC recharge
15 inch air compressor hose
Includes: 12 volt ac/dc power cord, 120 volt ac/dc adapter/power cord & air inflator nozzle adapter set
Dimensions in inches: 12.5H x 11W x 7.5D

GaryG