On long warm days everything in the bags gets very hot, I keep my flip flops on the bottom in my saddle bag and they get very warm uncomfortable to wear right away.
I find the left side bag to be much cooler than the right side bag due to the fact that the head pipes exit the engine on the right. I put clothing in the right bag and the wife's cosmetics and other temperature sensitive stuff in the left one.
Seems like one of the soft sided coolers might work with cold packs. Yeti is supposed to be coming out with some soft sided ones that would probably be excellent based on their other products if they make one small enough. But I agree with the idea of a small cooler on the back.
We traveled 4 hours with an icepack in an insulated bag for my boyfriend's insulin in Florida heat. When we arrived at the hotel it was still cold but careful not to freeze it. Wrap the insulin in facecloths so it doesn't touch the ice.
The bags do get quite hot, I lined the bottom of mine with some light covered foam rubber, take big freezer bags and use frozen sponges than use a small soft cooler to store stuff and holds quite well for 4-6 hours of riding...Carried a friends insulin and it was quite cold inside the soft cooler bag stuffed with ice packs...And no mess...My SG is black...