Maybe someone should help build a site to help this?

In my neighborhood something like this is already getting started on Nextdoor. Not a great tool for organizing people, but it's better than nothing.

Better yet, teach elders how to buy groceries online.

That works as far as it goes. The problem that we're starting to see is empty shelves. While at the store recently, I saw one of the store shoppers looking at an empty shelf muttering "I don't even know what to substitute here..."