I favour "lifeboat rations" these are high energy compressed biscuits with a long shelf life and are intended to be eaten straight from the pack.
One packet is said to last one person three days, but that is presuming little activity as would be the case in a lifeboat.
A day and a half from each packet would IMHO be more realistic if hiking or otherwise exerting oneself.

I could suggest a UK supplier, but probably better to buy from somewhere in the USA.

I prefer the "seven oceans" brand, but others exist.