Yes, I bought an "ice cube" cooler (it's blue) at Target. It's not big, it holds a little more than two 1/2 gallon ice cream containers, but it does just barely fit under the cargo cover.
I'm pretty sure it's this one:
Amazon.com: Igloo #43058 Ice Cube 14 Cooler:...
By the way, I place it in the center of the cargo area to get it to fit properly. It doesn't fit well near eaither side.