Wooden Boat
The simplest vehicle in the game: set it on water, sit in it and row. So a lake stops being a wall on your first afternoon.
It floats and goes where you point it. No fuel, no damage, nothing to repair. Set it down on water, right-click to sit in it, and crouch to get out, the same as a pilot's seat.
Cheap and early on purpose: a boat you can't afford until you have a smelter would be a boat nobody builds. Essential on an Archipelago.