Hmm, that's tough.
If your husband is willing to stand up to her, then you can try that- but if he can't set a boundary, do you really want to be the one to do it?
I'd say just try to let go and recycle the coupons and the magazines and try not to let it bug you. Don't even bother with taking the stuff to another place, unless it is really easy- just recycle it all or dump it and make it easier for you to let go.
Tell your dh to absolutely refuse anything...