Reminder: you were born with it.
You do not need permission to be creative; you came into the world bundled with it.
1. layer 3 paper grocery bags together as a reusable grocery bag, by all means, DO IT.
2. And if you want to tape the handles together, or staple the tops, or tape up the bottom and sides, GO AHEAD. It will probably work (it does), but even if it doesn’t (it will), DON’T WAIT FOR PERMISSION (you had it already, I just reminded you).
3. Just do it!