Let someone know where you're going and when you expect to return.
Get a full-service tuneup (recommended at 30,000 miles, 60,000 and so on). Bring your car in for service at least a week or two before you plan to leave - don't wait until the day before.
Check your car battery terminals for corrosion. Terminals can be cleaned with a wire brush dipped in baking soda and water. Add distilled water to the battery (if applicable - some batteries are sealed).
Have the battery "load tested" if it's more than 4 years old. Replace if it's close to 5 years old or older.
Inspect your tire-tread wear and maintain the proper air pressure indicated in your owner's manual.
Examine the radiator for leaks. Have the radiator "pressure checked" for leaks that are not obvious on a visual inspection.
Have your mechanic check for "play" in the water pump.
Check the coolant strength in the radiator overflow reservoir with a hydrometer. The antifreeze should be clean and up to the proper level.
Replace the coolant and/or flush the cooling system if this hasn't been done in the last 15,000 miles.
Examine all belts and hoses associated with your cooling system carefully. Make sure there are no cracks or leaks. Replace any you have doubts about, and carry extras.
Make a habit of watching the temperature gauge. Turn off the air conditioning if the engine temperature gets too high.
Check all the car's fluids: oil, coolant, brake fluid, power steering and automatic transmission fluid (if applicable), hydraulic clutch fluid (if applicable) and windshield washer fluid.
Change the oil and oil filter - it should be changed every 3,000 miles.
Be certain your headlights, taillights, brake lights and turning signals work, and replace bulbs as necessary.
Bring a map of your destination as well as maps that show the best way to get there. Many auto insurance agents offer free maps, or you can purchase them at gas stations and convenience stores.
Check your tires, making sure they're properly inflated and have plenty of tread.
Check that your spare tire, jack and tire tools are in good working condition.
Put air in the spare tire.
Carry extra oil, water, antifreeze, ATF and brake fluid in the trunk of your car.