If it has not been serviced in a while change the spark plug leeds, same with auto fluid, often the trans and diff are neglected.
Dont forget the battery and washer bottle,
flush radiator and replace thermostate if it hasnt been done.
This all depends on how often it has been replaced.
you got 2 weeks off, do the lot and you know it has all been done and on the next service just change oil and filter,
Do not put any additives to the fuel, they could cause you more probs with fuel pumps, injectors etc,
Fuel injector cleaners are a waste of money and dont do anything, the only way to clean injectors is to remove and get them cleaned and flow tested, they will usually put new caps (for clean spray pattern) and seals, and also drip test them, You should do these at about 100,000km's,
Dont clean throttle body while you wait for oil to drain as you need the car running to do this.(no oil = seized engine)
A better way of doing this is by removing the plenum chamber and cleaning of carbon deposits with carby clean, spraying it in there wont do much.