The easiest one to do is National Night Out.
You can pretty much show up on that one and they will find you something to do but it's best to sign up.
Depends on the store of course, mine was suburban so there was a fair number active members in charities and other projects.
We did walkithons, and other fund raising events you could sign up for if you had sponsors.
There was also the school library rebuild at an designated (usually urban school).
I volunteered for that, got picked, took the day off, and then was dumped at the last minute.
Since all the people who did go were ETLs and TLs, I can guess why.