Here's a bit of info that affects gas purchase at ARCO (and many other gas stations and fast food places) - if you use your debit card you will have to pay a fee of 40 - 70 cents per transaction.
So, you can get gas at ARCO with your debit card but you'll pay a 45 cent surcharge or something like that. Same with Taco Bell, for example, use your debit card and pay a fee.
It isn't like that in Colorado at all so it was a shock for me out there. I think businesses pay higher fees or something so they pass them along to consumers. I'm sure they're all paying more in taxes but it's still not something I anticipated until I arrived. Cash is always better for best prices in CA.