For example, the main ingredient in gasoline is C8H18. It has good energy density at atmospheric pressure, and the fire risks are manageable. We already use carbon/hydrogen systems today!

I think one of the candidates for metal hydride fuel cells is MgH2? It apparently also has decent energy density. Of course, magnesium poses some risks of its own. And I personally have no idea what a complete supply chain and refueling system would look like, or what it would cost.

Still, I fully expect that any portable energy storage is going to come with tradeoffs: cost, pollution, rare materials, and always the risk of catastrophic discharge (via fire, explosion, or messy kinetic failures). We should pursue multiple alternatives and invest in basic science, because portable energy is incredibly useful.