If it's a sticky point with you then I suggest telling whoever rides with you that you would like some money before the trip.
I myself am easy going. If you help with the gas cool, if not..no biggie I was going caving anyway. The one thing I do require is either bring your own drinks or help chip in on the drinks in the cooler.. We stop at Wal-Mart and get a 12 pack or two of the Bubba colas or Root Beer which cost about 3.00 dollars a 12 pack so it comes out to about a dollar a piece.