Hook

Most people wait on cave skeletons for this, but piranhas drop it too, and in the jungle they swim in surface water you can reach on day one. A short walk along a jungle river will usually turn one up long before you have the gear to survive the cavern layer, and getting hook mobility that early changes how fast the rest of the world opens up.

If a spare turns up, build the second grappling hook rather than selling loose parts. The finished tool is worth many times what a vendor pays for the components separately.