We also went to the event last night. It was fantastic, hands down delightful. I don't think I can think of a single negative thing to say about it other than that we got there too early (around 525 pm) and had to wait around for the 6 pm start time that was VERY clearly communicated to us.
For snacks, as others have pointed out, there was popcorn, ice cream bars and sandwiches, each available in 3-4 locations around the park. Fruit (apples and grapes) I only saw in one place, but they were welcome, precleaned, and ready to eat. Very nice. There was food for sale and, having been to H2O Glow Nights the week before, they used the same menu for this event. Which means make sure to buy a Miss Tilly sipper while you are there!
I must have missed the characters. I saw Chip and Dale dancing at a party over by the Crush 'N Gusher, but I didn't see any of the character meet and greets. Maybe they were in the kid area?
Lines were phenomenally short for most of the night. Being there at 6 possibly provided the shortest lines. We walked on to many, many water slides. I did see some lines a couple of times, but usually just walked away, came back in an hour, and walked onto the slide. It stretches credulity how many water slides I rode in a 5 hour visit. AND we spent significant time in the lazy river, AND they had some of the special floats out.
Towels were free and plentiful. Pop into the gift shop and they were set up with lots of towels and can give you as many as you need. Then, drop them in the towel return when you're done.
My only advice is for you to have a great time, and if you see a line that looks long, it's probably not long but go do something else and come back later and it should be shorter.