I purchased tickets online prior to our visit and had to print them out at home and carry them around our whole trip (two tickets, so two 8.5x11 pieces of paper that don't fit in a lanyard). I was worried I was going to lose or damage them. Also, the scanner they have at the entry gates is terrible...the line to enter the park really backed up because they were having trouble scanning the "tickets" like ours. I was annoyed that they couldn't somehow transfer our ticket information onto our room keys.
As another poster said, the Express Passes are a separate item, a small paper card. These cards to fit in the lanyards, and if I remember correctely, if you positioned them with your picture facing out, you do not have to take them out of the lanyard.
The ticket situation was probably the most (and really only) frustrating aspect of our visit, especially because of how it backed up the lines for park entry. But, if you get there early (I would say at least 30 min before the park is supposed to open), you still shouldn't have to wait long. Maybe they have upgraded the ticket scanners since last November.
You can take snacks and water bottles into the parks, but with each passing day, I found myself taking less and less with me. This is because you have to store everything in a locker to go on many of the rides. Having all of that extra stuff just became a liability, so I had incentive to pare down. We did buy one of the freestyle mugs and carried that around for drinks, though. Our first day in the park, we stopped to have a late breakfast at Leaky Cauldron. The hostess there automatically rang up our order as part of a "meal plan" (I don't know what all this includes since I never looked it up), but we did end up with some beverage "credits." I used these to get the freestyle mug at about 1/2 of the regular cost, and then we purchased the unlimited refills the other days we were in the parks. It was very easy for two people to share this mug, and since I don't drink any caffeine, this was pretty much my only option if I wanted carbonated beverages.