Don't register at grocery stores.
A typical voter registration form, including the ones handed out at tables, is designed to be mailed in. If you just hand it to a stranger sitting at a table, you're asking for it. There are people on both sides playing dirty right now. Constant vigilance!
If you can't get to a library or post office, there is a universal registration form available here.
If you live in some states, it's too late. In others, it isn't. For example, you can still register in California.
This has been a non-partisan public service announcement.