Unfortunately not; there's no way for third-party apps like RTM to run in the background (which would be necessary to make this feature work reliably), so there's no support for this built-in.

What I've done is to get in the habit of opening RTM when I go to the grocery/supermarket/shopping mall to see what I've tagged nearby. I don't always remember, but it really does help keep track of the not-super-important items I should probably buy at first chance. :)