You might want to search the archives - I know there have been a few posts about this topic. Here are some ideas:
Dancing in the GF lobby, to the orchestra
Watching the MK fireworks from the Grand One yacht
Having chocolate covered strawberries & champagne delivered to your room as a surprise
Walking along the beach from the GF to the Polynesian at night, past the wedding pavilion
Going for a carriage ride at the Wilderness Lodge
Doing something unique, like parasailing
Having dinner at V&A's
Eating at Narcoossee's during the MK fireworks, and watching the castle change colors while you have dinner
Staying concierge level!
Cheers!
Heather W