After going through many soft sided coolers for boating, I've landed on this Igloo 36 Marine as my favorite.

It strikes a good balance of price point, easy access, light weight, and decent insulation for a soft cooler.

Downsides would be, it might be a bit large for a kayak, and recent versions seem to be using cheaper smaller zippers that might be less robust than the original version. Still overall, I think it's a nice all around soft cooler for on the water day trips.