the high altitude isnt really an issue, the tanks are pressurised so the fuel wont boil. and a bit of Fuel system icing inhibitor (FSII) deals with the temperature. (combined wth the heated fuel recirc from the engines)

Thing is gas turbines will run on pretty much anything (up to and including coal dust), so the fuel only really has to meet certain standards ie flamability, corrosion/lubrication issues, and freezing. other than that its as cheap as humanly possible.

you honestly think the aviation industry would be paying for expensive well refined high quality fuels (let alone the military)