If fish are left to get warm the flesh will quickly go soft/mushy
We always take an icey tek cool box even in the winter. In the winter your squid stays frozen in the box so if not used it can go back in the freezer when home. During the summer put a load of ice/packs frozen bottles or even better flaked or crushed ice in there then when you catch fish they can go in and stay in tip top condition all day.
When we go to Alderney, the box packed with ice will keep fish in tip top condition for 4 or 5 days
The added bonus is that beer is also always cool
Martin