Just take this as a rambling of an idiot if you don't like the ideas. XD
1. Allow a person to row a boat at a slightly faster speed in exchange for using up stamina. (much like running)
2. It would be cool to introduce hostile animals for swamp biomes. like a crocodile.
3. a type of bug spray to combat minges. it could use foragables or metal for the can. so that it's not easily farmable. It would give a buff that makes it so minges don't damage you for a period of time.