Does using up leftovers in the fridge count as decluttering? I'm clearing out some of the containers and putting them back into the cupboard. As much as possible I store food in reusable containers (Rubbermaid, poor-man's-Tupperware from restaurants, jars with screw on lids, canning jars with reused lids and rings, etc.) I try not to use as much foil or plastic wrap as I used to, though I have upped the amount of parchment since getting the lifetime-supply-sized boxes at Costco. It's a lot easier to put down that paper than it is to grease and flour a pan, or just grease a pan, or for that matter to chip off something from a pan you didn't grease because you didn't think you had to. (Don't let cookies cool on the pan).

One thing I don't use much of any more is Tupperware. It's just too damned expensive for what it does. Rubbermaid won my heart over with their stacking containers and red lids that click together if you need that stability in the stack. And some of the no-name plastic items I find at The Container Store (I go there for special shaped containers).