Even though my kids are grown I still always seem to have a bag with me when I am at Disney World.
I always have things that I "need" in the park, like ponchos and sunglasses and hand sanitizer. Sometimes my bag is a small crossbody and sometimes it is a packed to the gills backpack. I don't think I've ever gone into a park at Disney World without some sort of bag.
But, what happens when you're touring? Can you bring your bags on rides at Disney World?
Thankfully - nearly every attraction at Disney World is designed so you can bring your bag with you while you ride. Even on the roller coasters there is room around your feet or you'll find mesh bags attached to the seat in front of you where you can stash your stuff.
Unlike other parks (I'm looking at you Universal) being able to keep your bags with you and not needing to store them in a locker for every attraction saves you lots of time and a ton of hassle.
In fact, the only attraction where there are lockers nearby is also the only attraction we recommend you DO use a locker, and that is for Kali River Rapids at Animal Kingdom.
Near the entrance to Kali you will find lockers that are free to use. Kali River Rapids is notorious for soaking you. Every time I have ever ridden it at least 1 person (and usually multiple people) have wound up totally soaked. And, even if your bag is small, unless you can get it 100% safely under a poncho we say don't even try it - put it in a locker, instead. The same holds true for your electronics like cell phones and cameras. Store those safely in a locker where you can guarantee they will stay dry.
There are a couple of other attractions where you and your bags might get wet. Splash Mountain and even sometimes Pirates have been known to get their riders quite wet. If you plan on riding those attractions make a plan for what to do with your bags.
On those rides I usually just set my bag on top of my feet. That keeps it off the floor (where any water might pool) and relatively dry.
If you have any high dollar equipment that you want to protect, you can also stash your stuff in one of the super giant Ziplock storage bags and then set it on your feet. Or even a cheap poncho wrapped around it would probably do the trick. If you don't have a bag but you DO have a cell phone, you might want to think about carrying a baggie with you to store it in on attractions like Splash Mountain (or to use to protect your phone in case of rain).
Soarin' is one attraction where you may find your bag won't fit in the provided space. On that ride, you are asked to store your bags under your seat, however, the storage space is kind of small. But don't worry!
If your bag wont fit the Cast Members will just ask you to leave it on the floor in front of you. After you are safely buckled in they will move your bag a few feet to the side where you can pick it up after it is over.
One thing we do NOT advise is that you leave your bags in or hooked onto your stroller. Please do not do that!
I know Disney is magical and you may feel like your stuff is safe but the fact is that theft DOES happen at Disney World. If you spend any time at all on Disney message boards you'll read story after story about people having their bags stolen out of their stroller, or, worse, their entire stroller stolen. Don't leave anything in your stroller that you wouldn't be okay losing.
So, there you go! Rest assured that if you're planning on taking a bag or backpack with you into the parks at Disney World, 99.9% of the time you'll be able to keep with you!
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