Racing or DE?
Most (all) tracks have air readily available. Just invest in a good gauge and maybe an air line (but again they usually have one readily available).
For pressure at DE, keep a good log of where you set cold PSI to first thing in AM. Then check pressure immediately coming off each session and quickly adjust down to where you ideally want to end. Once you know delta you can easily set cold PSI before starting day (based on conditions) and really shouldn't need to adjust too much from there except for extremes.
That said, I carry a Slime branded kit with compressor like the Superflow MV-50 in link provided above. This is the JIC for my trailer and tow vehicle en route.
Good luck
