There are three different kinds of fossils that paleontologists look for: body fossils, trace fossils, and cast and mold fossils.

Body fossils can be bones like a fossils skeleton or it can be a shell-like an ammonite fossil. Things like coprolite (fossilized poop!) and burrows are examples of trace fossils, they are evidence of life that was once there. Cast and mold fossils are exactly what they sound like, impressions left behind by organic material, these could be footprints or outlines of a leaf. You also do not have to bake this activity, you can leave them out to dry. This can take a few days to be completely dry, flipping to the other side periodically.