Other Travel Considerations
No matter how far you're traveling to the marathon, make sure you arrive in plenty of time. Allow for possible airline or traffic delays so you don't feel rushed. If you're traveling to another time zone, particularly one with a time difference of more than 1 hour, give yourself time to arrive and acclimate.
The same holds if you'll be running in an environment significantly different from the one you're used to training in. For example, if you live in Maine and you're running a December marathon in Hawaii, try to arrive there at least a week prior to the race to acclimate as much as possible to the higher temperature and humidity you'll experience during the race. Acclimating to heat and humidity takes a minimum of a week.
Know Where You're Going
Try to find a hotel close to the start and finish of the race. If they're all beyond your budget, are already booked, or you want to stay with a friend or family member in the area, map out how you're going to get to the race start in plenty of time.
Better yet, drive to the start location the day before to make sure you know the best roads to get there and where you will park. Oftentimes, roads near the course are closed the day of the marathon, thus limiting your access to the start of the race.
Be sure to carefully read all official marathon literature prior to the event to familiarize yourself with procedures (documentation you need to obtain your race number, such as a photo ID, road closures, start and finish line procedures, location of aid stations and portable toilets, and shuttle bus schedules, to name just a few). Don't assume the marathon starting line will be set up adjacent to the site of race headquarters on the day prior (where registration and an exposition is often held), or you will be in for a big shock.