As already discussed, days the event is held change.
As far as what to expect:
A type of cookie and softdrink - last year the cookie was a rice crispy treat snow man and the soft drink was cider.
Beer and wine is extra.
Some games for kids (geared around 3+ to 6 or 7 year olds usually).
A character dressed as santa or an elf.
Usually an ornament also but they sometimes run out and the line to get the ornament is occasionally very long (all depending how lucky you are when you get there).
Generally a low key event with some things to do and other
DVC'ers to meet. Not a carnival type event with loads of stuff to do, but nice.
It can at times get very crowded, no one really controls that aspect, it depends when everybody feels liek showing up and leaving.