Since most science fiction vehicles don't run on unleaded gasoline, would you even know what to fill the tank with if you were lucky enough to get behind the wheel? With everything out there from warp cores to specialized space fuel, here's a handy list that lets you know what powers some of the more popular vehicles around the galaxy, just in case you find yourself stranded and need to call AAA.
Any vehicle from the Star Trek Universe: Dilithium Crystals. This is an element created just for Star Trek that powers everything from the U.S.S. Enterprise to a Klingon Bird of Prey. Dilithium had to be mined, just like we have to drill for oil, and could be hard to come by. Of course, when Star Trek: The Next Generation came out the writers decided to just cheat and make it something that they could make synthetically, thereby killing any future "we're out of gas!" storylines.
The Time-Traveling Delorean from Back to the Future: plutonium, gas, and/or garbage. Doc Brown's time-tripping Delorean actually has an engine that does run on gas, although when he came back from the future he'd converted the flux capacitor to run on a Mr. Fusion device, thereby eliminating the need for plutonium pellets for driving through the decades. Just toss some trash inside, and you're good to go.
Anything in the Battlestar Galactica universe: Tylium. In the world of BSG, both Cylon and Human ships run off of a fictional ore called tylium. It's only found on certain planets, and has to be mined, just like dilithium crystals. But unlike the crystals, it also has to be refined and turned into a gasoline like substance. No idea what kind of mileage you get out of it, but it also powers their "faster than light" drives, so it must pack quite a punch.
The TARDIS from Doctor Who: artificial black holes, radiation, life force... take your pick. The TARDIS in the world of Doctor Who looks like a giant blue phonebooth, and travels through both time and space. However it's actually a sentient being that draws its power from one of several different sources, depending on what season of the show you're watching. In the current incarnation of the show, the Doctor has to stop periodically near a space-time rift and suck up the leaking radiation in order to keep things going. A sort of interstellar pit stop, if you will. Photo by lizardian.
The Spaceship Heart of Gold from The Hitchhiker's Guide To The Galaxy: a cup of hot tea. The Heart of Gold ran on an infinite improbability drive that took it through "every point in the universe at once" when it was switched on. Not too shabby. All it took was an electronic brain and a good Brownian motion generator, like a cup of tea, and you're off. Probably the cheapest form of travel ever invented.
Anything in Star Wars: your guess is as good as ours. While you sometimes see strange hoses and gizmos hooked to the ships before they launch, it was never made clear in these movies what they run on. George Lucas apparently never wanted us to get bored by the details, so you could fill in the blanks on your own for this one. Lando was running a gas-mining facility on Bespin in The Empire Strikes back, so maybe he was in the spaceship fuel business. We may never know, so be careful with whatever you put in the tank of your X-Wing.
As always, extinguish all smoking materials while refueling and be sure to hold on to your receipts. Your own mileage may vary.