Okay - I'm assuming since we're both in IL the flight will be about as long as it was for us - maybe an extra half hour.
By the time you take off, get your obligatory peanuts and beverage, consume said "snack", pass off to the flight attendant, and stow the tray in its upright position, you're ready to land again. It was REALLY fast! (Even flying with three kids and being pregnant - it was fast)
Rattles won't distract other people on the flight - our kids had to YELL to talk to us because the plane was quite loud. The only thing that will upset someone on the plane is a child running around with sticky fingers or MAYBE a baby crying. But, most people totally understand a crying baby and know that we're doing our best. We heard so many "they did SO well!" comments and not one wicked glance from a fellow traveller.
As for your packing - having travelled with the kids extensively, I can say that you are 100% certainly overpacking

I know, it's really easy to do. An extra outfit here, a "what if it gets cold" there...and before you know it the suitcase is stocked. Take my word for it - skip the extras. If it isn't something you use on a daily basis at home, don't worry about it.
Here is what I would do to your list, for a 9 month old:
1>Clothes Am/PM per day (going in October tends to get chilly at night)
This will be a tremendous amount of extra clothes. Instead, get a good zip-up hooded jacket. We got nice fleece ones from Gymboree for the kids and if it was REALLY cold they'd wear a turtleneck underneath, a sweatshirt, then the jacket. But, I could just throw the jackets in the backpack incase it got chilly and they can wear them over anything. October - I wouldn't count on much chilly weather...even at night. The crowd keeps you warm and you're landlocked - so no ocean breeze or anything to be concerned with. The *only* time we were cold at Disney was in December and it was about 11PM before it was cold enough to need hats/mittens.
So, ultimately - bring a zip up hooded jacket (so you can leave it open if it's really too warm) and a small crib-sized blanket - at largest.
2>
MNSSHP costume and holloween t-shirt and jeans to change into when she gets bothered by costume
If you think she's going to be bothered by the costume, you might want to pick something else for the costume. Especially for MNSSHP, which can be hot/crowded/rushed AND long.
3>Diapers*
Over-packed these, big time last trip. We ended up having to haul a whole (unopened) pack back home with us. Are you stopping at a grocery store at all? Renting a car? Can one of you take a cab to do a quick shopping trip? There's a walgreens, wal-mart, sam's, and Target (man I love that Target!) right on the main strip.
4>Formula*
ditto - we don't use formula, but if I did, I'd be packing the most concentrated form possible - I think most of the manufacturers make packets of powdered formula now that are easily portable. BRING YOUR OWN WATER - I can't drink the tap water there - makes me physically ill. Throw a bottle of water in the diaper bag and mix the formula in the bottle. Not worth the risk that the baby will get sick from all the sulphur.
5>wipes*
ditto - see diapers
6>Food*
At 9 months, you shouldn't have too much trouble finding food for her onsite. We asked everywhere we went last trip and never had trouble finding a banana, applesauce, steamed veggies (carrots, green beans, peas), baked potatoes (plain), yogurt, and lots of pasta cut into teensy bits. We were almost always able to feed her from our plate and dealing with jarred food and spoons would have been too much of a hassle for us. Of course, I packed them - but they were unopened and brought back home.
7>Pocket Bibsters*
Another one that we don't use at home, so we didn't bring them. No problems. Lots of baby wipes on hand, packed a lightweight bib that could be rinsed off and re-used (Bumkins).
8>Disposable Spoons*
you can almost always get a regular spoon at the restaurant...or feed off a fork.
9> Can of lysol to disinfect nasty changing tables
I didn't find a single changing table that was nasty in the park - not that you can always see the germs, but nothing like Wal-Mart has, kwim? The diaper bag changing pad works great and is far more comfortable.
10>ziplock baggies for wet clothes and dirty diapers
Again, most good diaper bags will have a dirty duds bag..and throw the diapers away in the bathroom (another thing we brought - sassy disposable diaper bags - and didn't use once)
11>Pack of White onsies (go with everything)
if this is something you use all the time, only
12>Purell for before we change, touch, feed the baby
You're better off washing your hands than touching/feeding the baby with all the toxins in that stuff.
13>swim suit and jumbo pack of little swimmers diaper pants
Little Swimmers can be reused - they do not absorb anything, and only hold in the solid waste. Just hang them up to dry. Better yet - get a reusable swim diaper. Target has sets - cute tops and swim diaper bottoms on clearance right now for about $3 - way less than the little swimmers and you won't need more than one per day you swim, even IF you throw them away.
14>Stroller
think high-end umbrella with recline - Maclaren Quest was our favorite so far (out of 9 strollers we've owned and taken on trips)
15>CAr Seat - infant? If you can, bring an infant seat. MUCH easier to deal with. If you have to bring a convertible, use a carrying bag and check it for the plane. SOOO not worth it to deal with installing, only to have them fuss because they're in there, etc. It's very difficult to get on and off a plane with a baby and a diaper bag as it is - add a stroller and a carseat, people start "accidentally" bumping into you. And pre-boarding is a joke...never enough time. Plus there's no room in the seats to buckle the carseat in properly, unless it's an infant. This was our biggest headache.
16>rain pncho thing for stroller
Just a rain guard, right? Our Macs came with rain guards and they're nice and flat. If so, do this. If not, take your chances - it may not even rain the time you're there, and if it does, are you really going to be walking around in the rain with the baby? We usually duck in to a store or restaurant.
17>Shoes, socks, sun hats, sandals
Does she walk? If she's going to be walking on the ground at the park, sure - protective foot wear is good. But, if she's just cruising - or barely standing - she won't need them. If you want something for keeping on socks or helping her to develop her leg muscles, try
www.robeez.com or
www.jackandlily.com - they're much better for babies' feet than "shoes".
18>Diaper rash cream - call the manufacturer and see if they can send you a few samples. That's what we brought and didn't need them.
19> Teething ring - if you bring this, bring something to keep her from throwing it on the ground
20>baby orajel - Hylands teething tablets work better...orajel is washed off in a few seconds by the overproduction of saliva that teething causes. If there is inflammation, tylenol will be better
21>Those add a link rings by fisher price
22>Rubber bath duckies for bath time (2) - we didn't have time for long baths - pretty much just get them in and get them out. Days are very long and very busy at WDW
23>Disposable bath mitts with soap already in them - brought these, too - used one or two. Next time I'll be bringing a head-to-toe wash in a little travel shampoo bottle and using the onsite washcloths.
24>bottles & nipples - no experience here, but you might want to try the take and toss bottles that, if lost (or not cleaned because you'll be in the park) you don't have to worry about funky stuff being in the bottle.
25>Sun block - it wasn't that much more expensive in the parks, but we love the aerosol stuff that came out this year - white bottle - Coppertone? purple lid. SAVES SOOO much time!