I use a polar bear cooler, it straps to the top of my top box or fits perfectly in the bottom of Ventura bag that sits on my seat when solo.
They are not cheap but they do work.
I prefer to use frozen water bottles to keep things cool as the water can be useful for other things.
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.