Yes - we always stop off at Costco on the way back to the airport - it's one of the cheapest places to fill up on petrol. Also they accept Amex which is better than the UK where you have to pay by Switch.
When we went prior to Christmas we got some fabulous cheapo Christmas presents and it was well worth the trip. At other times it was the same old stuff they have in the UK, pretty much. Also, I would say thst it was almost identical in style, size (and often the stuff sold) than the one I use here in Manchester, so don't necessarily expect it to be much different to what you're used to.