Hey there! Well for Rock N Roller Coaster, they're more lenient towards the bag issue, as there are even pouches in the trains. For Dragons, if it can't go around your waist (like a fanny pack) then it's got to go in a locker. So for you having a fanny pack, its alright. It is hard on my part having to tell guests to use a locker (I don't like inconveniencing them, and I have had VERY rude guests say curse words and such to me about it). But if you do get to the load platform, and you have a loose article, we're not allowed to hold it. Soooo, you will be sent alll the back to the locker to put it away. Best to put it in a locker before you start to queue.
Reason for it all is that it's a big safety issue. If those bags or loose articles become dislodged from you somehow and go flying, they could cause some damage if they hit someone.