Although, pound for pound, hydrogen has the highest chemical fuel storage (sorry kerosene), and you can buy hydrogen reactors for producing electricity (like the Brunton Hydrogen Reactor priced for a reasonable $149.99), actually, thorium is probably the best (known) source of stored (nuclear) power. It's about 250 times more efficient than plutonium. And 1 lb of thorium has about the same amount of stored energy as seventeen thousand 300 gallon tanks of kerosene! Thorium is safe enough to hold, so you don't have to build anything to store it... talk about efficient! Of course, you will need an nuclear reactor to make use of it.
This is not as crazy as it sounds... here's a plan from Instructables for building one in your home: Build A Fusion Reactor. I mean this is what DIY Home Improvement is all about!
Also here's a picture of a thorium powered concept car from Cadillac:
