Second the gas buddy recommendation. But last time we visited Oahu we wanted to fill up at Costco and found the gas station and parking lot to be a complete cluster. Used gas buddy to find a nearby alternative option and gladly paid 10-20 cents a gallon more for zero wait and zero chaos (we generally rent econoboxes on the islands since we don’t need the space or power of a larger vehicle).

My local Costco doesn’t have gas, so I am not very experienced with it, but from other horror stories it seems that it’s not an unusual experience.