It depends on what the forecast is when we go. I get crazy about checking the forecast over and over as my countdown gets closer. If there is a "slight chance of showers" and it is in the warmer summer months, I bring along those tiny folded up ponchos, they fit in my fanny pack. Not the "trash bag" ones from the dollar store but the nice "camping type" ones that have their own pouch. They work well and you are not too hot wearing them. The dollar ones have short sleeves so they are basically worthless. Once in a while, in good weather, I even take the poncho for dd(6)who is afraid of getting wet on splash and grizzly-lol.
If it is winter and the forecast calls for rain, we do the whole "serious" raincoat thing and umbrellas too. Last Jan, it poured and poured on us and no poncho was going to keep us dry or warm. I brought a backpack with the raincoats and planned to put them in a locker if needed but as soon as we got there, the drizzle started, we ran and rode both Alice rides (because they close in the ran) and we were the last people off before it started to pour and pour.
Before we got there, I knew there was a good chance so we did have spare shoes in the hotel and in the late afternoon when the rain had stopped, we all went and changed our shoes because as hard as it was raining, it was 3 inches deep on the ground. Still, because we were prepared, it was fine and we still had a really good time until the fireworks-lol. It stopped raining and we were all lined up and sure enough, it started raining again just as the fireworks were to start and they cancelled them.
I really felt sorry for the people who were not prepared, they were drenched and miserable. We saw little kids shivering in just t-shirts, babies in strollers soaked through, tons of people 1/2 wet in torn DL ponchos and even quite a few people wearing big green trash bags. I guess the bags and ponchos would work for light rain but this was like a monsoon. I talked to some teenagers who were wet and freezing but had been dropped off by their moms and had hours to wait until they got picked up. They were callling their moms over and over but no one answered and they were almost crying cause the sweatshirts cost more than they had.
One thing though, be prepared for jealous looks because people really want your umbrella when it rains that hard. Standing in line with raincoats and umbrellas while it is pouring rain and others have nothing is not real popular. We did offer to share our umbrellas with our fellow waiters but they were all pretty much soaked anyway!
I always take the tiny foldup ones, about 5 inches long and if it isn't raining yet and we put the stuff in the locker, I can still fit a couple of umbrellas in the fanny pack. Then I can use them walking back to the lockers in the rain which is always a madhouse because tons of people put their rain gear in the lockers too-lol.
(DH insisted he didn't need anything but his poncho and he was soaked but just trooped on-lol and no, I didn't say, "well, I told you so.") I know my kids well and had they gotten wet and cold, that would have been the end of it and mommy would have been the one crying cause we had to leave dl!
In the fall and winter when there is no rain forecast, I usually bring a backpack with sweatshirts and sweatpants for the kids. The days are nice enough, sometimes the kids can even wear shorts, but when it gets dark, we get cold! We go to the locker and get the backpack and I slip the sweatpants right over whatever they are wearing and put on the sweatshirts. I even do this when we stay "on property" because no one wants to ever leave and go back to the hotel to change-lol.
In Nov, I was pretty cold and had a t-shirt, cashmere sweater, polar fleece coat and gloves and scarf! If you are not going to stay until midnight, not such a big deal but usually after around 8 or so, we HAVE to hit the locker.
We are going again in Nov right before Thanksgiving and I am hoping NO RAIN. The cold we can deal with, but the rain was bad. Contrary to what we had read, the crowds did NOT thin out. I guess when so many tourist pay to come from far away, they are not leaving just because it rains.