Make a list
Start listing out the things you will need a week before you leave. Take in to account the destination and plan what you will need. If you are going to the mountains make sure to take warm clothing and if you are going camping you will need more planning. List out essential items such as medication and tick off each item as you pack.
Pack for emergencies
Make sure you have the tool box and a flashlight in the car in the event of a car break down, check on the condition of the spare tire. Pack a first aid box which is well stocked.
Be prepared for weather changes. Have extra, suitable clothes for adverse weather, pack in rain coats and umbrellas.
Carry enough snacks for the trip, especially if you are travelling with children. Take sandwiches, easy to eat fruits such as apples, bananas and berries. Take plenty of water and fluids to keep you hydrated during the long trip.