fuel prices
Depending on your aircraft, just try to pay cash and watch what happens. I fly air ambulance and was a a small airport where thry didn't take any of the company credit cards I had. The look on the fueler's face ( this was a weekend, so he was the only one there) when I whipped out $1200 in cash was as they say in the credit card ads, priceless. Especially when he refused it.