1: Digging up berry bushes and transplanting them (shovel). This preserves the resource but allows you to have them where you want them, perhaps requiring originating biome to stay alive. So basically you could get all the bushes from an area and keep them in one spot there...set a portal. Saves time in the long run. (Maybe make the plant not able to portal like ore and ingots)

2: Vikings used natural resources for dishes and stuff. So being able to make a large variety of plates, bowls and whatnot would be cool. Maybe require the bowls for crafting some meals.

3: Thirst. Player should have to drink fluids, in the same vein as food.

4: Horses. Vikings used horses and spread them world wide. Having wild horses on the plains and meadows would be amazing.

5: Odin's gift. When Odin appears in front of the player ( rare event ) he should give them a small limited buff. Seeing one's God would be inspiring.

6: Total overhaul of the random map gen, including options for players to tweak some of the settings.

7: Difficulty slider that scales mob health/stamina and damage - for players that want a harder experience.

8: Ability to apply war paint that gives small bonuses to the character.

9: Converting 50 of the same trophy to a repelling head on a stick (repels the specific monster). Has a small radius, cannot be placed in same area as another head regardless of type. Ability to put them on the cart or tacked to the side of your mount's saddle. (like the Witcher 3)

10: Magic in the form of rituals and runes. Nothing crazy though.

11: Wounds, bandages and limb damage for player and mobs both. Shoot a troll in the knee and watch him limp towards you.

12: Weapon poisons, arrow poisons. (no more ice, poison, fire arrows - would have to make the poisons then apply it)

I could go on all night hahaha. Anyway, here's a few idea's. The head in the cart was suggested in a different thread, it was not my idea. :)