I throw my leftover pizza in bread wrappers; keeps everything in and it's re-using it.

As for popcorn, I use the old pot-and-stove technique. It's noisy, but tastes great, once I drizzle in melted butter and toss with nutritional yeast (tastes cheesy)/Tapatio powder/salad seasoning/whatever interesting herb blends I found at the natural foods co-op's bulk spices section.

I remember Alton Brown has a recipe for homemade microwave popcorn; I'd be happy to find it if anyone's interested.