It's Florida, so there's going to be rain in the forecast. And, it probably will rain. Fortunately, the rain in Florida (more times than not) does not hang around too long.
During our past few trips we have only had one or two days where it rained most of the day, but we go during December and that's the "dry" month.
I'd recommend panchos - they have worked for my family. I don't wear the panchos - with the humidity I often feel too hot. I actually invested in a nice North Face rain jacket that I bring down every year (and am wearing today in NY!)
My biggest recommendation - find some shoes that are good for the rain and will keep your feet dry. Whether you go with some boat shoes (and go sans sock) or actually wear the vintage LL Bean boots is your choice. But, if it's going to rain, I'd recommend investing in a pair! Nothing, and I mean NOTHING is worse than walking around with wet socks. It poured one day on our last trip. I don't mind wet clothes (well, I do, but not as much!) but socks take a very long time to dry.
Outside of this, use the rain to your advantage. Stay up to date with the weather forecast. If it's only going to rain for an hour - use this to your advantage. During rain showers, many people will leave the park. It's in your best interest to hop in a store or see a show. If it's the afternoon, use the time to grab lunch.
You don't have to see a specific show - if you're at MK, try the Carousel of Progress or an indoor ride like POTC.
If it's raining in the morning, know when it's bound to stop (check the weather and the radar) and leave your hotel around an hour before it's scheduled to stop. By doing so, you can beat the crowds to the park. Many people will wait until it STOPS, then head over. But, if it's not coming down too hard, start to head over and hang out under the bus stop (or another concealed area.) Once it stops, head to your number one ride. It will be a lower wait time - but not for long!