I usually go paddling in Mid-May, where temps can go from freezing to hot, all in the same day.
I troll as I paddle and if the weather is warm, this is what I do to keep fish cool and edible.
I did it in 2006, and paddled all day in 80 degree temps and the fish was fine for supper that night.
Fillet/gut fish and put in appropriate size zip lock bag. Go to bank and get a couple of the canvas money bags they give customers for change.
I soak bag and secured shut with a Bungee Dealee Bob and put under my seat out of the sun.
About every half-hour, I re- soak the bag.
You would do the same thing overnight, except you wouldn't have to re-soak bag, just soak it good, and hang with food pack or separate,  the bag needs to be free to evaporate to keep the fish cool.
Unless it was during the hottest part of the paddling season, I think this would work just fine.
Others on here put fish in watertight containers and anchor offshore in cold water.
I think in hotter weather, that would be the ticket, but if the night temps are say 60 degrees or less, I think you'd be okay?
Of course, being fish there's no guarantee's and you should do what you feel most comfortable with ;)