I use Amazon.com: Mabis Dmi Healthcare Ice Bags - Large, 11 Inch, Blue, One: Health & Personal Care

It holds a ton of ice, fills quickly, and the water stays frozen for a surprisingly long time. It's never leaked a drop, and doesn't even 'sweat.' Being able to refill at hotel ice machines is key for me. This is the model I've used, and it's been bulletproof.