I almost always fill up. Last night, oilBabe and I went out in two cars because I'm on-call this week and need to be able to respond if something happens.
So we both need gas. Her car was empty and mine was 1/2 full. So it took $64 to fill her car, and another $28 to fill mine.
She said it was painful to fill up, so I asked her why she lets it get to empty if it's so painful to see $70 to fill up the Camry. She said because she was avoiding getting gas in IL. We were in MO (St. Louis, south county for those in the know) and gas is $0.25/gallon cheaper than in IL.
I do the same, I try to avoid filling up in IL, since gas is significantly cheaper in MO.
I don't make special trips to MO to fill up. So the only time I'll not fill up is if I know I'm going to MO soon, and need some gas to get there. Then, I'll put $10 or $20 in the tank until I can get there.
But I try to get gas when I'm at 1/2 a tank, so the shock at the pump isn't so great. My tank is only 13.2 gallons, so 7 gallons or $30 worth is not so heart stopping, LOL.