Some simple foods:

I'm not sure if fermented foods are really paleo, but as there is saurkraut recipe, I'll give this:

Fermented fish from Finland's Savo/Kainuu region

Caution: don't let the fish touch the ground, or really anything, or it may caught botulism, and it won't be nice. In Norway there died 3 people in 30 year period from eating fermented fish, so it's probably not very big risk.

Ingredients:
Fish (this should not be extremely lean fish, like pickerel for example, it should have atleast as much fat as roach)
Rye flour (optional, this just speeds the fermentation process, and results in different tasting fish)
Salt (also optional)

Take out innards of the fish, leave the kidneys intact, also take off the laminas and head. You can either leave the bones intact or take them off. Don't wash it, but you can rub out some mucus if you want, but the final result is not as strong then.

Now take some wooden/glass/plastic sterile barrel. It's best if you can use some that has air-tight cover to it, but it also should be small enough so you can put something heavy on it so it will put some weight on the fish. Now just put some flour in the barrel, put some fish on it, then some salt, then some flour, then some fish, then some salt etc. until you've used all your fish. Put the cover on and take some sterile weight and put it on the cover. Let sit in warm place for 3 days, then for some weeks in little bit colder environment. The fish has turned red when it's ready, and the meat will separate from the bones very easily.

If you don't want to use any salt and/or flour, just leave them out. I won't take any responsibility if you die after eating this, maybe I forgot some vital part of this recipe.

Boiled organs:

Take liver, kidney, tongue and/or heart. Boil until they/it suit your preferences on softness etc. Put some salt and/or fat on them if you want. Liver and kidneys don't need much boiling of course.. use the boiling water for soups.

Fish soup:

Ingredients:
Everything that's left from a fish after the filets have been cut off, expect entrails. The fish should be big enough, weighing maybe atleast 1kg.

Cut big heads in two parts. Simmer fish parts in water for maybe 15 minutes, take them off the water. Separate all meats you can from the fish heads and other parts, including eyes (you may eat them separately if you want). But the bones back in the water, simmer for about an hour (this shouldn't be done according to laws of culinarists, but nah, it just gives some different flavours to it, I'll say. I'm not sure if this is wise thing to do with very fatty fish, as the fats may oxidize too much). Percolate the water. If you want to use veggies put them there now. Simmer or boil until veggies are soft enough for you. Put the meats in there. Season with whatever you want. Purée.

It's messy and takes some time, but it's a good way to use fish heads and other stuff like that.

Edit: the fish weight (1kg) is for the whole fish before the filets are cut off.