Collect a set of fossils to display, or throw them into a crafting grid for an alternative source of Bonemeal.
There are five varieties to collect, found in various biomes. They're few and far between, but each fossil provides multiple Bonemeal when processed on the crafting grid.
I wanted an easy alternative to Bones for Bonemeal that didn't involve Skeletons or or Compost. They're also fun to dig up and somewhat realistic.
If you have any additional ides for fossil variety or location let me know in the comments.