personally, I can't imagine shopping there, I know that even coffee is overpriced, since I've worked in a store, well percentage wise, I suppose there is a high demand for it so it evens out, still the material you use costs about 10/20 cents, the coffee costs a dollar, why? nobody knows, it's how you make a buck.
It's mostly regulations and requirements, for some reason you need a lot of papers to sell anything, so why not charge extra.
Highway stops are a mess, it's like people are waiting for your car to die off so they can make some thousands hauling that to the shop and fixing it, so since you can probably spend a couple of thousands when something goes wrong, why not charge 10 times as much for a sandwich, I think nobody shops there and they have to make up for that in prices, maybe 5% of people can stop and have a coffee at a gas station, personally I feel bad, sure the cups are porcelain but still it's like a 
star restaurant
well you have some views and it's nice, humm I guess come prepared, have a water tank and a boiler some filters and a few porcelain cups in the car :)
Thanks for your experiences and your good advice!