When riding Greyhound for trips longer than a day this is what I do.....!
1) Pack light - Bring the essentials and plan to do laundry while you are at WDW.
2) In your carry on have lots of things to occupy your time.
*books and a clip on book light (that overhead light that shines down it to bright and will distribute other neighbors sleeping
*Portable CD player with head phone (lots of batteries)\
*Soft side CD holder (filled with your favorite CD)
*Toothbrush and Toothpaste (during your meal stops you will be greatful to have this
*Travel Pillow (you can get a small one of these a Wal-Mart or Target near you)
*Travel Blanket (not a thick blanket off your bed) a fleece blanket of some sort this bus airconditioning gets really cold
*Soft Side Cooler with Soda (not a huges cooler) just a small enough to handle a few beverages
*BABY WIPES (you can wash your hands with these - can says enough about baby wipes
*Snack and treats (trail mix, granola bars, chocolate for those stressful moments - snacks from the machine can be expensive
*DONT USE THE SAME SIZE CARRY ON YOU WOULD FOR AN AIRPLANE. The Height of the Carry should be half the size of the airplane one or it won't fit in the overhead and you will have to check it.
3) Get luggage tags and keep you check bags tickets where you can find them
4) If you change buses, be very proactive and make sure you bags change buses with you - check and double check again - don't expect Greyhound staff to do that for you.
Remember to note the time the driver state the bus will depart when you stop for your meal breaks....they will leave you if you are not back on the bus.
Also, keep an open mind and don't be mindful of your belongs (i.e. don't leave your purse laying on your seat while you go to the bathroom). Just use common sense and you will be fine! Have a great , safe trip and give us a trip report when you return.