Give your people a quick synopsis of what to expect (as far as what to wear).
Some cleats, if they have em, if not, old running shoes. I've actually seen guys roll out to the field first time wearing boat shoes, crocs, new shoes... just let them know they're going to get them dirty lol.
Most paint doesn't stain nowadays, but heed warning some might. I'd stay away from wearing black/really dark clothing if it's hot.
Old hat headband or beanie is nice to keep sweat out the eyes.
You ought to supply a couple rolls of toilet paper or buy a pack of cheap shop towels to wipe off mask lenses. Makes for a bad day not being able to see!
Extra change of socks, always keep a fresh pair for the drive home!
Have fun! Most importantly!