This is not something I really know about so I have been trying to find out for you.
My first thought was that presumably it is just really important to make sure fuel is stored in the right way so that it is insulated from extreme temperatures. But it depends what kind of fuel you are using, as different materials will freeze, boil or even explode in very different conditions or even just when exposed to other gases.
According to NASA, ( you can follow this link if you like) [http://www.nasa.gov/topics/technology/hydrogen/hydrogen_fuel_of_choice.html], Liquid Hydrogen is one of the favourites. This is tricky to work with because you need it in a liquid form to use as fuel, but it is only liquid at really really low temperatures, so they actually need to keep it really cold to be useful for them!
Hope that helps!
Hey mcnab! Cool question – that’s not something I’ve ever thought about before!
Space travel requires very special types of fuel – nothing like the petrol we put in our cars. As Julie said, the most common space fuel is liquid hydrogen. This is hydrogen that has been made so cold it has condensed into a liquid. It happens at a temperature of -252 degrees C! So in space it actually has to be prevented from heating up by the sun and turning back to a gas (this would probably be catastrophic – the expansion from liquid to gas would likely explode the container it’s in!).