The answer is simple - most cars nowadays will hold enough fuel and are efficient enough, that if you fill up before you leave, you won't need to re-fill part way through your journey.
If, like me, you begrudge paying the over-inflated prices (irrespective of whether they're justified or not), then simply use the service stations for the toilets and nothing else.
If I'm going somewhere that will involve me driving for more than an hour or so, I'll usually make sure I have drinks in the car and have something to eat before I set off and possibly still have a snack in the car, just in case I get peckish.
No one is forcing you to pay these prices; so either plan ahead, or pay up ..... simple :)