I'm looking for the easiest way to cook or preserve fish at the river or lakeside with as minimal preparation or cooking involved so they can be eaten later. Mainly trout, pike or walleye. Ideally I could find a way to cook/pickle them almost instantly without having to gut them (I'm inexperienced in this regard) and then refrigerate them once home.
I'm not concerned about taste too much, just keeping the fish safe to eat. My idea was to clean, remove the head, tail and scales, wash them again and just throw them into a thermos with hot water, salt and vinegar and leave them for a few hours to cook thoroughly, then refrigerate them.
The water I would be fishing in is not the cleanest however (Amstel river in The Netherlands), so I'm still concerned about health and safety. I think it might be necessary to also do a rudimentary fileting (i.e just chop off everything except the edible meat) and then throw the meat into a thermos. However as I'm not experienced with gutting this would be a very unskilled effort I'm not sure this is risk-proof.
So I thought I'd ask to see if anyone knows of the right way to approach this, I'm sure there must be a quick, simple if inelegant/unappetizing way to preserve a fish at the riverside. Surely there's a survival technique that can get a fish from water to fridge/plate with as minimal effort and risk as possible?