I've not done it yet, but it will probably happen sooner or later. It will be a very expensive bottle of milk!
What I did do a couple of months ago, having completed my mum's online shop for her (i started this when Covid first struck), was accidently delete the whole order including the slot. I thought I was deleting the slot for the following work, and only realized my mistake after pressing 'confirm'
.
Needless to say, there were no slots whatsoever available for the same day when I tried to re-book.
I always stick two bottles of whisky in Mum's trolley to reserve her slot, then delete them when I complete it. At least if I ever forget to complete it, she will be able to drown her sorrows 