You can donate grocery coupons (including expired ones) to military families.
Our local post offices have donation boxes on their counters. Then they get the coupons to military bases - they use them at the PX or Commissary - they accept the expired ones up to 6 months past the date.
If your local PO doesn't do this, ask them why not
You can also look at the
Coupon Program, but then you have to mail them yourself.