We just got back from WDW with our DD who is almost three so older than what you're asking about but we took her when she was 18 months as well so that's closer. I can't help you much on the milk question because but I do have a few other kiddo tips that have helped us a lot. I just posted this in a post on another forum about how we organized our room at Pop so I'm going to copy and paste it here because having our room organized helped us so much having a little one with us. These are mostly tips that I accumulated on the boards myself but it kind of wraps them up.
On the side of the bathroom door facing the sink, I hung one of those shoe rack things for toiletries, sunscreen, meds, anything like that and it was a lifesaver. It kept all that junk easily accessible instead of in a bag but it was OFF the sink top. I got one of those things you hang from a closet rail to sort of make shelves and this gave us TONS of room for socks, underwear, t shirts and all of DD's clothes. There are only 3 small drawers in the dresser in the room so this totally saved us. I hung it all the way over on the end of the close by the safe. Next to that I had a pop up laundry hamper. Also AWESOME for keeping dirty clothes from being in a random pile somewhere. We used the rest of the closet for the few hanging things we had and there were plenty of hangers for us, although I had been prepared to ask for more if necessary. On the shelf above the hanging bar, we had a diaper box and three of those closet maid square bin things. In one of them, I had dishes (sippy cups, emergency nap pacis, cereal bowls, etc.). The second was kind of house keeping stuff (Lysol wipes, a Ziploc full of clothespins that came in handy, boxes of large and small ziplocs, grocery bags for poopy dipes, papertowels etc.) The third bin was for the stuff I needed to replenish our park backpack each day (gum, glow sticks, hand sanitizer, etc.). There was just enough room for those items and a few other small things to be stashed up there. On the counter next to the sink, I brought a small dollar store plastic tub with holes in the sides for dirty dishes and then I used that when I washed. I filled the sink with dish soapy water, washed, and moved everything to the tub, then emptied the sink and rinsed the dishes and tub. I had some cheapo dish towels that could hang on the edge of that tub when not in use. We also brought a small foldable stool so DD could wash her hands by herself. DH thought that was crazy but it was so worth it. Also a help was a small plug in night light for right by the sink for nighttime. In the two small cubbies in the "dresser" I used one for a diaper changing supply area (we are having some potty training issues so our doctor recommended we give her a break on the trip) and the other for swim stuff (towels, suits, floaties) after it had time to dry. One of the cubbies in one bedside table was filled with our snacks and breakfast stuff that didn't need the fridge and the other cubby was for the few toys and books that we brought along. I brought a power strip and plugged it in by the small table so our electronics tended to accumulate there but since it wasn't covered with too much other junk, this was okay. We rented a stroller from Kingdom Strollers (highly recommended!) and because of the king bed, there was plenty of room to park it in front of the window. Also, I brought a Minnie dress up magnet kit and DD could play with it on the back of the door while we were getting ready or otherwise busy. I'm not sure why but this really kept her entertained.
That's probably way more detail than you wanted but I was pretty proud of it. It was my opus. And it really made our week at Pop go much more smoothly.
So that was that. Another thing that worked for us was a little diaper bag/back pack strategy. We used a regular (actually my old college) back pack for a diaper bag but it can get full and heavy quickly. We learned to use large ziplocs to split out some of the things in the bag and then leave them in the storage thing under the stroller. We left these unsupervised so there is some trust there but we didn't have problems with it. I wouldn't leave anything valuable though. I'm talking things like extra diapers and wipes, a change of clothes and shoes, sunscreen, the rain cover for the stroller, etc. Then the backpack was lighter and easier to carry onto rides or into restaurants and we could return to get what we need from the stroller. Here's the trick to this though. To get on a bus or parking lot tram, you have to fold the stroller up which is a pain with all that stuff underneath. So we traveled with a clear bag they give you in the stores or food courts so I could quickly throw all the stuff into it and fold up the stroller. We would wait until after we went through bag check to take the stuff out of that bag because they can check it without having to open it and dig around. After bag check, I could quickly empty this into the bottom of the stroller and we'd be on our way until we needed something. I know we could have just taken less stuff but with kids sometimes it's better to feel like you're prepared for anything.
We drive from Kentucky so I have a little experience with that too. I second the driving at night thing. My husband is a paramedic and works 24 hour shifts so he's used to that. We let DD watch DVD movies or listen to Disney cds and if it's dark out, she's way more likely to fall asleep. We usually try to eat on the road and then I change her into jammies and she'll usually drift off pretty quickly. I have a little pillow I can prop her head up with after she's drifted off because I hate watching it flop to the side for hours.
I mentioned it above but some sort of magnet toy is great in the room because the doors are metal. DD doesn't care much about the magnets on our fridge at home or anything but was obsessed with it in our room. Go figure!
I hope that helps. Good luck!
