Check your car owner's manual
Check engine oil
To check the engine oil, park the car on a level spot, warm up and stop the engine. Wait for a minute to allow the oil to drain down the oil pan. Pull the engine oil dipstick out, wipe it with a clean rag or a paper towel and insert it back fully. Pull it out again and check the level - it should be close to the "FULL" mark on the dipstick.
If the engine oil appears too black, it's better to change it now. If the level is low, you can top it up using the same type of oil as you already have in the engine.
If you notice that your car consumes a notable amount of engine oil between oil changes, it's a good idea to take some spare engine oil with you on a trip. Many engine problems are caused by lack of oil changes. If your next oil change is due soon, definitely do it before the trip.
Check the automatic transmission fluid
A long trip with a full load will be another exam for your automatic transmission. If your transmission fluid change is due soon, do it before a trip.
Here is how to check the transmission fluid if your car has a transmission dipstick (some
cars don't have a dipstick):
Visually check engine coolant (antifreeze) in the overflow tank
Visually check the engine coolant level in the overflow tank. Your owner's manual has the directions. The level should be between "Low" and "Full" marks.
(Don't open the radiator cap or the pressurized overflow tank cap when the engine is hot!)
If the coolant level is just a bit low, you can top it up using recommended type of coolant mixed with water. Again, your owner's manual has the proper way to do it. If the coolant level is well below the "Low" mark, have your cooling system checked for leaks. Any leaks should be fixed before a trip, as lack of coolant on the road may cause the engine to overheat which may result in serious damage.
Make sure the battery terminals are tight and not corroded. Corroded terminals will cause troubles.
Unfortunately, there is no way to tell when the battery will die; sometimes it happens unexpectedly with no prior signs. However, if you feel that when you are starting the car, the engine cranks slower than normally, the battery is probably close to its end. Usually a new battery may last from 3 to 6 years, so if your battery is 4-5 year old, it's a good idea to have it tested before a trip.