I've been contemplating taking a really small bag. If I go really small, I'd take a Lizzy (I don't have a mini-hipster - I don't think the flap would work for me and I'm not sure if it would fit my sunglasses). My camera is much too big for a Lizzy, but a thin camera might fit. If I go with a medium bag, I'd try taking the Libby. My camera and camcorder would fit in that. If I go with a big bag, I'd take my Cargo Sling. This is big enough to fit souvenirs and a couple of water bottles, cameras, ponchos, etc. It's pretty roomy. All of these go cross-body, which is what I like. And they all zip shut.
I thought about trying a large Hipster, but it didn't feel right on me when it was loaded up. It's a flat bag, and it seemed to bulge weirdly if I put too much in it.
I have a Hipster, Wristlet, Amy, On the Go, Mini-Hip Bag and various other Vera Bags. I forgot ALL of them (except my wristlet) for my trip last month!

(I had planned on using a backpack for my daughter, but ended up leaving it with my mom to use instead.)
I ended up going off-property, looking for a mini-hipster. I found them...but I also found the
Lizzy, which has wider, adjustable straps (the mini-hipster does not).
I REALLY LOVED my Lizzy for carrying through the parks. I have a large-ish camera (Canon G10) and it fit fine in the main compartment, along with Mentos Gum, my Inhaler, and my headphones. I usually wear my sunglasses on my head, but they also fit in the purse when I needed to go on a ride.
I put all of my "wallet stuff" in the back zipper pouch that has credit card slots. I also stored my fastpasses (with the most current one on top) in those slots.
The front 'flap pouch' has an ID holder, perfect for my PhotoPass Card.
There is another pouch pocket between the flap pocket and the main compartment...that's where I stored my iPhone.
This has become my new favorite small bag! The straps are cross-body, but I also wore it as a waist bag...it was nice to give my back a break!