I have a combo jump starter/air compressor. I'm carrying it in my Volt now because my 2013 (manufactured in 2012) is still on it's original battery and I'm just waiting for it to die... it's a little larger than the OE air compressor but not much, I'm thinking seriously about modifying the pocket the OE air compressor sits in since I don't carry the EVSE with me anymore.
edit - can't recommend mine anymore as I bought it on clearance and it seems to be out of production, but it is a "Husky" branded version of this, I forgot to mention it has an Inverter too - the main reason I was shopping for it in the first place! https://www.amazon.com/STANLEY-FATMAX-PPRH7DS-Professional-Station/dp/B01DLYQ4DS/
I have been using this for years and it has never let me down. Disclaimer though I have only used the Jumpstart function once but it worked fine. Mainly use it to provide power and fill tires.