A mortar and pestle: Have each item crafted separately. Use it to crush small amounts of things like stone to gravel. Also expand what we can crush with the mill like make gunpowder by crushing coal, chilli powder by crushing chillies. The mortar and pestle would be used like the tanning rack and the hunting knife.
A sled or wagon we can drag behind the horse or pull ourselves: This has no place in the game as there is a large inventory, but it could prove useful if you are clearing a massive part of a forest.
Food Spoilage: as it is right now it is too easy to get food. Even with farming there is a certain point when you have enough food that farming is pointless.
Diseases: for more realism. Eating rotten food, not taking care of your wounds properly, and even getting attacked by an infected animal could cause a disease. Use the mortar and pestle with a few plants could make a medicine to counteract it.
The world is not dangerous enough: Add sharks in the salt water, wolves where there are sheep, add snakes, spiders, scorpions, octopuses, squid, Lions.
Other peaceful animals: Fish
Animal Husbandry: Catching animals with a net, carrying them to a pen, feed them and give them water, build a trough for both water and food. Breed them with animals of the opposite sex, raise the children, eventually slaughter them for meat and hide, or trade them to other players or NPCs. also milk the cows and goats.
I'll make another thread for cooking ideas and recipes.
I assume many of these ideas are already in the plans somewhere.