As they are asking people to shop as infrequently as possible, I think it makes sense to take the car and get all your groceries in one go.
We went to our Tesco last evening at about 6pm, as the last stop on our daily walk. They have organised a very efficient queueing system, with yellow lines 2m apart painted across the (fenced off) car park for about 100m, then yellow blobs for the rest of the car park. There are workers manning the queues and making sure people stand in the right places. The queue moved fairly quickly, and there was a lot of good humour. We queued no more than 10 minutes before we were allowed into the shop. They were doing a "five in, five out" system.
Inside, where the self scanners are located, they had a sanitising station set up, so you can sanitise the trolley, scanner etc.
It was quite late in the day, I suppose, so there were no eggs, flour, pasta, rice, cleaning things or loo rolls, but plenty of fresh fruit and vegetables, meat and other things.
I kind of wish they'd stick to the same policy when all this is over. It was very civilised!