Check with the airline to see size limits on carry on baggage. The size of bag used depends on size limits of the airline and the limits of how much the passenger can carry. While it's important to pack everything needed in the carry on bag, it's also important to consider the limits of how much the passenger can carry for long periods of time, especially if a layover is expected.
Use a notebook and pen to write down what is to be included in the carry on bag. If small children are going to be flying with an adult, it's easiest to include things the child may need int the adult's bag as opposed to having the child carry his or her own bag. Be sure to include a full change of clothes including underwear and socks, all toiletries and medicines to be brought on the trip. A cell phone and cash are also good to pack in the carry on bag.
Gather together all the items to be packed in the carry on bag and place them inside the bag to ensure all items will fit. Put clothes in first, as these are typically the last item needed, and add more items to the bag according to how important the items are and when they will be needed. Pack a cell phone, cash, and boarding passes last, as these will typically be needed first and are important. If small children are flying, be sure to include their things toward the top of the bag as well, or place all of the children's items in a separate compartment.
