OP aside from delivery slots have you looked at local Facebook Covid groups in your area?
Where i live volunteers (I'm one btw) have signed up with the Council and we are delivering shopping to shielded/vulnerable members of the local community.
I'm not sure how every council is working but in my location we are being allocated to a single household (which I think makes sense as you are dealing with the same person and they get to know what you like/need).
I call "my" household and they text me a shopping list and we agree substitutes if I can't get certain items etc. The reason for the text is to prove they've asked for what I have bought.
I then shop, deliver the shopping to the porch along with the receipt and they then pay me back via internet banking and send a confirmation text that I've delivered what they asked for.
All volunteers in my area have had to watch a safeguarding training video and sign a confidentiality agreement so as not to divulge anything about the identity/circumstances/shopping habits etc of the household we are assigned to (that also includes health issues if we are picking up prescriptions).
If you are really struggling it might be an option?
For the reasons above I can't say much but it's been a real privilege to help out the lovely household I've been assigned to and I'm glad I can make a difference in this awful situation.