Yellow Marigold

Picking one up is what convinces the Dye Trader to move in, and marigolds sit on ordinary surface grass from the first morning of a world. That makes him the fastest new resident available if you want him early.

A pickaxe is the only thing that will take one. Swinging a sword through the grass destroys the plant and leaves you nothing, which is the usual reason people think these are rare when they are everywhere. Spelunker Potions highlight them if you are gathering in bulk.

Run your pile through a Dye Vat before you sell. The finished dye is worth considerably more than the raw flower, and before you have anything better to unload it is a genuine early coin source.