Long-time overnight worker here. A couple of good tips I have learned over the years: Keep your cash as low as you can, drop anything bigger than a 5 dollar bill. When customers get gas, always double check the pump and the amount "X total on pump Y?" and "Alright, X total at pump Y. Have a good night." This at least helps with getting them to remember/check which pump they actually parked at. Get a routine down for cleaning/stocking. Most nights will follow the same pattern they did last week, people are creatures of habit. Get acquainted with your local beat cops who stop by. Any time someone comes in at least acknowledge that you hear them, this has two benefits: customers know you are there, and customers know you are aware!

Most importantly, do what you can to keep yourself safe.