Grocery stores should have a lane where they charge more, such as 5% more per item. It would be like a toll lane for people in a hurry.
I've actually considered leaving a note in my supermarket's suggestion box, to the effect that there should be a $1 congestion charge to enter the parking lot between 10am and 5pm on Saturday and Sunday. The wait in line doesn't bother me anywhere near as much as fruitlessly driving around the parking lot looking for someplace to park.
($1 is a starting point. The point being trial and error to hit the equilibrium of a moderately full parking lot at peak hours.)
I suspect this supermarket would actually not lose customers on net, because it is so much better than its competition that people previously deterred by the crowds would balance out people deterred by the congestion charge.
This thread is for discussing anything that doesn't seem to deserve its own post.
If the resulting discussion becomes impractical to continue here, it means the topic is a promising candidate for its own thread.