I am going to comment on the SLR camera on rides, as I am a photographer and sold cameras for a living until recently. If you don't have one already, I'd get a small bad strictly for your SLR and make it only JUST big enough to fit your SLR. I recommend Loepro if you don't have one already. They are the best of the best and have a lifetime guarantee. They have bags for about $20.99 called the topload zoom. The camera fits lens down into the bag and is perfect for easy access.
As far as taking photos on rides with the SLR in hand, I've never been to DL, but I know that rides like Big Thunder Mountain at WDW were fine if you're careful. I'd take plastic bags to wrap your camera bag in for water rides just in case. Loepro also makes bags that have all weather coverings.
They fit so much more into them than they look. I fit a cable knit hoodie into it weeks ago when I got too warm. I also had 2 water bottles, my camera, cell phone and a bunch of other little things into it. I really liked it. It wasn't too bulky and was easy to take on and off. On most rides I just moved it forward and had it on my lap.
DH carries the back pack with water bottles, snacks, sunscreen, baggies, and hand sanitizer. I wear my small purse with our APs, credit cards, camera, and hand held fan.