Oh, thank God! xD I thought I was only one who loved to play around in the worlds.
One thing I tend to do a lot is swim for no reason whatsoever.
I also love going to Pooh's storybook in that one place with the hill and the swing, and dive off the hill into the creek. There's also swimming as far as you can in that same creek to see how far you can go before leaving that page.
Then there's that page with the big tree; I like going to the highest branch I can and jumping into the small pool of water. That's kind of challenging due to the size of the mini lake, and the fact that the leaves on the tree makes it impossible to tell where it is when you're up that high.
There was one thing I found entertaining on Captain Hook's ship (this only works after your trip to Hollow Bastion); get on deck, and a bunch of Dark Balls will appear. While they're still slowly showing up, quickly jump your way up to the very top of the deck (where the White Trinity is). Most of the time, from what I've seen, the Dark Balls will NOT follow you. Instead, they will stay where they first appeared and patrol that area as well as the space above the water near that area. To watch them, stand on top of the box-things behind the desk, or on the side of the ship (there's room to stand). Sometimes, the Dark Balls will be hovering above the water just below where you're standing, AND STILL NOT NOTICE YOU THERE. xD It's fun standing there and just watching them patrol the area until they decide to disappear or catch sight of you.