All sailors should know about "Zeer Fridges".  Look up that term on Youtube.   It is an ancient evaporation fridge made out of 2 containers and some sand that uses wind and water to do the cooling.   Sailors normally have a fairly good supply of sand, wind and water.

Ancient Romans used Zeer Fridges on their ships.   It's just forgotten tech.

Also.. lightly coating your eggs with vaseline will help them stay fresher for up to 4 times as long. It's an old sailing trick. Eggs are porous and breath in air and water, this is why hard boiled eggs weigh more.

this is good for day sailing :-) if you eat that for a while ytou will be crazy !