I have this one by Detours. http://detours.us/store/rack-bags/

It has a shoulder strap, and also seems to be kind of insulated. I rode with ice cream recently, and it stayed frozen. I use this bag the most for commuting. It's a great size, yet unnoticeable when riding; attaches quickly and securely with velcro. I've fit a whole cake in it. I did find the strap too long, so I cut and shortened it.