Engine oil and oil filter require regular replacement:
we recommend every 3000 miles or every 12 months whichever comes first.
If your Air conditioning is no longer working the chances are it needs an re-gas. Some cars require a re-gas more frequently than others.
Coolant:
Engine coolant is absolutely necessary for the engine to function without damaging itself. You should check this frequently and book in to have this flushed and refilled at regular intervals.