It's a concept most adventurers understand not as a policy, but as a way of life. I first learned about it way back in the day of being a camp counselor for a killer local kids camp.
The concept is simple, leave the space you visit as pristine as you found it (if not even better). If successful, the next people shouldn't know you were there at all. The idea guarantees natural preservation for all who adventure in the future.
Leave No Trace, or "LNT" if you're REALLY into the spirit, is a way of life for the coffee truck as well. Whether it's curbside in Southern Maine, at a wedding in the mountains of New Hampshire, or down a side street in the city of Boston, we adhere ourselves to a strict "LNT" policy.
The only signs the coffee truck was even there should be photos, a slight caffeine buzz, and maybe a couple tire tracks.
This policy of ours will guarantee you have nothing to worry about with the coffee truck at your event, and will help us preserve all locations for future adventurers wherever they wander.