A Leveling System where you can Unlock Certain Things such as buildings and tools at a certain Level, like level 1 you can unlock a wooden axe and a pick axe then if you unlock a axe you can make a upgraded axe from stone, the same as the pick axe and you can unlock a level 1 campfire if you have a axe and a pick axe at level 1.
I don't really like the levelling system in general, specially if we're talking about "skills" that allows our player to improve their "combat techniques", speed, and so on.
Anyway, it might be interesting to make a leveling system which will allow us, for example, to gather more quickly, or give us more wood when cutting a tree.
Leveling system related to crafting system could be also interesting, but always considering that "high level" players don't have a huge advantage from "first level" players. A solution for this could be, anyway, introducing perma death: When the player is death, all the skills and levels die with him