Most of the WDW Resorts have a "Refillable Mug" program in their food court area (aka Fast Food-Counter Service). You purchase a mug for around $10.99 and are entitled to "free" or less expensive refills for the duration of your stay. The refills are available from the beverage dispensers and usually include: coffee, sodas, ice tea, and hot chocolate. No other purchase is required to get your mug or your refills.
The mugs have the hotel logo on them and signs state that they are for use at that hotel for the duration of your visit.
For an avid coffee or soda drinker, especially with the 'free' refills, you can't beat it.
The table below outlines the refillable mugs available at the resorts and the purchase as well as refill price. Be sure to add 6% tax to the purchase price.
I think the tax is now at 6.5% and I have to agree with the Previous poster, it makes no sense since you can only use them at the resort from which you purchased them. This program is not available in the 4 major parks.