Just back from Aulani and this is what I booked in advance:
-Aunty's free sessions ("themed experience")
-Ukelele lessons
-Family Fun Animation
-"Thingamabobs" a family experience on the beach (W and Sun AM right now)
-Aunty's premium experiences (Moana + "Celebrate summer"--birthday gifts)
-Wikiwiki braids at Painted Sky
-Character breakfast at Makahiki
While there we also made light up ears
They seem to leave available space for all of these things for day of--you can show up at the character breakfast at 7 and you should get in. I liked knowing I would be able to do the things, but it seems the flip side is show up early enough and you can still sign up--it took a couple days of trying to be able to do ears, mostly because the time they offered us kept conflicting with something else we had scheduled. They offered us something every day. I sprained my ankle and we ended up changing some of our plans and staying at the resort more and my kids were able to get into Aunty's each of those days day of. Hope that helps someone!