Re: stopping at a gas station and not spending anything --
I almost always seek out a Casey's if possible. I've given them (the company as a whole) so much business over the years that there's no way I'm going to feel guilty going in and taking a bathroom break without buying anything on that particular visit.
If an employee ever did question me, I'd just show them my Casey's credit card and tell them how many thousands of dollars I've spent in the last 20+ years. (this has never happened, though!)