Update!
Pietu stayed with me for a total of 66 days. He helped me hunt at least 7-10 elk/reindeer, 5 bears, 2 lynxes, and 1 wolf. He assisted me in finishing up my giant cabin, skinning, and roasting meat. Even though mechanically he didn't, I like to pretend he also helped me harvest my 700kg of turnips
At the end of our adventures, when time came to reward him, I tested how many goods he wanted. I gave him a northern spear at some point and couldn't get it back because he was wielding it, so I'm not sure if that item counts towards the final value. He seemed totally satisfied with 120 pieces of dried elk meat.
But for roleplay purposes I ended up giving him a fine bear fur, 50 dried elk meat, the aforementioned northern spear, and a bear tooth necklace. I like to think of us as good friends and I'll will be visiting him every once in a while, since he lives in a nearby village.
Next goal is to find another NPC companion and keep them around for a whole year!