I always carry a full install of Peppermint OS, on a 4GB bootable USB thumb drive with persistence.
Takes a minute or two to boot on most machines, but I've never run across a machine that it wouldn't perform adequately on. Drives IT departments crazy, BTW. They can't figure out what's going on. So, caveat emptor, if you're running a Linux session over someone's winders network or whatevs.
The whole trick to it, IMO, is figuring out how to boot this_or_that machine from a USB port. All computers handle this quite differently in BIOS.
It easy to do a full install to a bootable USB key with persistence -- but, it does require two USB thumb drives. Boot from the first Live USB drive. Then, install the OS to the second USB drive, just as you would to a HDD/SSD drive. Simple pimple!
I might also mention, some Linux OSs run hideously slow from a USB drive. I tried many, many OSs before settling on Peppermint OS. Just saying...