I LOVE my Kavu crossbody rope bag. They aren't very big but I was surprised how much I could fit. I love all of the different pockets and sippers. Highly recommend this bag. http://www.kavu.com/Product/923/Rope_Bag.aspx
I was also going to suggest a Vera Bradley. I found that a backpack works great with the toddler. Vera has a smaller backpack that seems to work great for us and I still carry diapers. I like that it is washable. If you get a sale you can get it 25-50% off.
I think my next bag to WDW will be a LUG. All shapes and sizes and love all the pockets. I've purchased several of their larger bags for overnight/travel purposes and been very pleased. I always get mine from QVC. Just enter "LUG" into search and a whole bunch come up. I like that they have videos too.
I LOVE my Kavu crossbody rope bag. They aren't very big but I was surprised how much I could fit. I love all of the different pockets and sippers. Highly recommend this bag. http://www.kavu.com/Product/923/Rope_Bag.aspx