As a start we will consider petrol and diesel, apart from the obvious that you have enough for your journey it is worth checking the whole fuel system at least once a year, diesel because it has a habit of finding paths and holes that most other fluids don't and petrol because if it does leak, a hot surface or spark can cause an explosion, I know I have been there with leaky carburettors dripping onto the exhaust pipe
First check the fuel tank,...