Unexpected item in the bagging area

I arrived at Mrs D's house to pick up a shopping list to buy some essential items for her from the supermarket. We ended up having a chat for about half an hour before we even started talking about shopping. Mrs D read out her hand written list to me and I typed the items into my phone notes. Fortunately Mrs D had thought about the likely scenario of the supermarket not stocking all of her requested items so had some suggestions for appropriate substitutes if it came to it. Unfortunately though, I hadn't totted up the likely spend in my head so had accidentally committed to too much shopping for the spending allowance I had of £20. Having chatted through her shopping list with her, I had a good idea of the items which were essential and the ones which were more nice to have, so with help from the supermarket assistant, I unscanned some items for putting back on the shelves to leave me with a good selection to take back to Mrs D. On arrival back at Mrs D's place she was sad to hear I couldn't grab all the items on the list but grateful for the ones I was able to get - so all in all a successful trip.