Mars has CO2 in the thin atmosphere and oxygen in the minerals also. For Titan there is just the oxygen in the water which certainly looks more abundant on Titan than on Mars. Get oxygen from Enceladus?
Hmmm… those toxic perchlorates on Mars are also used in making rocket fuel - oxidizer in solid rocket fuel. You can make methane on mars but not as an energy source I think.
And those lakes and rivers on titan are ethane and methane not gasoline – good as cryogenic rocket fuels used with liquid oxygen as your oxidizer.
No I would be looking for nuclear fuels on both mars and titan, though cooling looks more difficult on Mars. Sure it is cold on mars but you still need a coolant.