Like the title says, why are a few things in our universe named after chocolate?
For example, there are the Milky Way, galaxy and Mars.
Is there a reason for this or not? Or is it that the chocolates were named after them?
None of these things were named after chocolate.
The name comes from a Greek myth, at the end of which Hera - Zeus' wife - spills her breast milk. In places where the sky has not been affected by light pollution, the Milky Way looks like a milky-white streak. Hence the name.
The Greek word γαλαξίας (galaxias) is closely tied to the Milky Way (because, for a long, long time, other galaxies were considered nebulae - "island universes"). It's English translation is "milky one" - a nod to the same Greek myth.
The chocolate of the same name was introduced in 1960.
Mars was a Roman god, not a Greek one (his Greek equivalent is Ares, I think). The name dates back for millennia - indeed, the Greeks associated Ares with the planet.
The chocolate of the same name was introduced in 1932.