We have found we spend far less if we have a week long meal list. We plan 7 meals then buy just what is needed - it is actually quite relaxing to know you have the ingredients for 7 full meals.
I also tend to do the supermarket shopping as I don’t browse. It is always expensive if we both go to the supermarket. I have found recently if I go to the supermarket at 1pm it is very quiet with no queues at the tills - but keep this quiet!