This is a really fun way to help your child(ren) understand how long until your trip. DW and DS have made one for our last few trips, and they use pictures from previous WDW vacations to decorate each link. Here are some pictures of our most recent chain.
I think DW just used either Pages or Word. She dragged the photos over from iPhoto. She did each page "landscape" and divided the page into thirds lengthwise, then cut the pages into three strips. Each link makes us excited for the upcoming trip and reminds us of fun memories from past trips.