wet bag

I consider this a diaper bag essential because it's a place to store outfits and other things that have become covered in spit, pee, poop, etc. We have Skip Hop and Swaddlebees -- both are good. We also use the wet bag to store wet swim gear after a day at the pool. That said, you could also keep a big Ziploc in your diaper bag and that would work just fine.