The following tips are from the Better Business Bureau.
Preparing your car for travel is very important. Make sure your car is ready for the trip by checking all vital fluids such as the oil and coolant, and by visually inspecting your car for anything that looks out of place. It is always a good idea to double-check the coolant hoses and all belts on your car. Failures of these items are among the most common reasons that cars break down; but fortunately, they are inexpensive to replace.
Also, check your car's battery for signs of corrosion or cracks. If the battery is the "self-diagnosing" type with an indicator, make sure it is fully charged. An older, weak battery may fail without much warning. If your battery has cracks, the fluid could leak from one or more cells, rendering it too weak to start your car. If you are taking an extended trip, or if your car has not been serviced recently, you should have it checked by a reputable mechanic before leaving. A good mechanic can usually spot the problems in advance, and advise you on how long you can delay a repair and what the consequences of not immediately repairing your car may be.