Chrome manufactured a limited number of "kozmo" bags. These are insulated full size bike messenger bags. They go on ebay for 80-120 dollars a piece and are worth it.
I pick up hot take out food in ours and then bike home twenty minutes and its still hot when I get home. I've thrown in a pile of cold veggies, milk etc into it without a problem.
This bag can hold more than you can carry.
http://search.ebay.com/search/search...zmo&category0=