Wow, you have some stingy friends. $10 for a ride to the grocery store?!? My friends with cars don't even charge for rides to the airport 40 minutes away!
I don't understand why everyone here seems to think that $10 is reasonable. Generally when you charge someone for gas money, the idea is that they pay you for the amount of gas that the trip used. If a 5-minute car trip requires $10 worth of gas, you probably might want to invest in a new car.
That being said, I've never owned a car (and have zero expectation of owning a car until I can pay for one) and I frequently just walk places. There's usually an alternative route that doesn't involve going along a highway.