People generally don't think "hey I want a $3 soda" and end up buying some gas. They need gas and get sold a $3 soda. By controlling the charging Tesla controls the customer. Given Tesla's fanatical desire to control everything, I don't think they'll be happy leasing out space in the corner of somebody else's gas station. At some point, they'll have a little free time to develop some kind of convenience store model and incorporate it into what, maybe 50K charging centers/RT depots/convenience stores. Lots of lottery tickets out there to be sold.
With pre-ordering from the in car screen so your order is bagged up and ready to go when you run in to use the restroom.