The O.P. SAK is an odor proof (including bears), water tight, durable, re-usable bag.  Good for food, diapers, toiletries, or garbage storage.  I've also seen them at REI.

http://www.watchfuleyedesigns.com/index.cfm?do=detail&productid=23

Clip-n-Seal bag clips

A nice compliment to the OP SAK is a Clip-n-seal bag clip as it adds an extra level of security to the "zip-loc" type closure on the OP Saks.

http://www.clip-n-seal.com/index.htm

These seem to have good utility both in bear country and to control in-vehicle odors in general.

I usually pre-prep my meals, removing extra wrappers, boxes, and only bringing the amount that I need.  Once de-packaged and measured I store each meal in zip-loc freezer bags along with any cooking instructions I might need.  I'm going to continue that practice, only use these bags in place of the freezer bag.  They are heavy enough that they should be re-usable.

I'll continue to keep my trash in freezer bags, but will double bag them with a couple of the larger OP SAKs to contain the odors.

In bear country, one of the smaller ones will be used to contain toiletries, larger ones can be used to store clothes that have been worn while cooking, etc.

Some of this isn't as relavent when car-camping in large groups.