Depends how tired you are - as most of the above posters have suggested, DTD, PI, shopping, etc. Also worth considering
if you have a hire car or don't mind extortionist cab fares, are dinner shows such as
Dixie Stampede,
Arabian Nights (if you're into horses, otherwise be warned the storyline is very thin) or
Medieval Times. Avoid Pirates like the plague - no story, bad food, so dull!
Also out and about (translation: off-property), especially this october, you've got
Universal's Halloween Horror Nights if you're into that sort of thing, or just a slow drive up and down the length of International Drive - start at the bottom end with the Premium Outlet complex, then work your way up one side, stopping at anything that takes your fancy (gift shops, wonderworks, ripleys, the mercado, pointe orlando etc), turn round when you get to (what used to be called) Belz Outlets and come down the other side and do the same! Should occupy some time!
Don't forget you've also got
Old Town - they open till 9 / 10 pm. Every saturday night they have a classic car cruise.
Hope that helps!