Hey Diane! I am so excited for you guys to see Mary Poppins, wish we lived closer to New York we'd be there in a heartbeat with rates that low, can't wait to hear all about it!!!! What a great DH you have to surprise you with that.
As for the bags, wow you must have been reading my mind (again, hey, great minds DO think alike : ) because I was thinking through the same things today. Here is what we are going to do, we learned after our fans were stolen on day 1.
I will carry my Vera Bradly backpack and in it bandaids, passes, id's,antibacterial wipes,AND the kids pin lanyards (my kids don't keep them on all day), and our camera (this year it will be our small video camera too - hopefully it will all fit.
In ANOTHER bag (typically it's a smaller/midsize beach bag type bag) to store under our stroller (we're bringing an umbrella one for Lauren- Volo- great stroller) in it will be:
the poncho's (we put 3 in here and that's it, Tim refuses to wear them : )
and the sunscreen, 3-4 bottles of water (they are frozen, put them in the freezer in the room the night before). that's all this bag holds so if it gets stolen it's not the end of the world. We will buy 2 more spray fans this year (sigh) and I plan on putting those under the bag at the bottom of the stroller tucked away. Last year we had them hanging from the back of the rental,- bad move on a 99 degree day

I would never want to lug those onto rides.
Last year Luke picked up a small hand held teenie mickey battery powered fan, and I found a tinkerbell one for 3.99 at Target for Lauren today. They have little lanyards on them, so I plan on having the kids carry their own teenie fans and those will be no problem for them to carry,and if they get sick of them I'll throw them in my purse.
As for a souvie budget- we did 75 per kid last year and it worked out well. Lauren used it to get her face painted, get some of those fancy minnie/sparkly ears with the veil type stuff hanging down and some jewlery stuff. Luke used his money on a McQueen tattoo, a Yeti shirt, and I forget what else. Typically we will front them the money for some things like I got Luke a pin for riding Rockin' Roller Coaster for the first time,etc. but they know what money they have and when it's gone it's gone and they've always been good with that. I plan on getting more stuff for our disney kitchen. I got the wine glasses last year they are AWESOME! Tim is the big spender in our family - he loves the Club Mickey store : ) Actually I can go nuts in the World of
Disney store too. Gotta get our yearly album, souvies for relatives back home (small stuff), gifts for people caring for our pets while we are away, etc.
Man did I just ramble on or what!! hope I helped some.
Lesley