Of course, my experience differs from most since I drive to Orlando in mid-December for Christmas with my parents and then stay on through mid-January ... but, I can't recommend this ENOUGH. In your carry-on bag, bring your shoes and your race-day necessities, but then bring (and CHECK) everything else.
In 2016 for Dopey, it poured during the 10K - so the night before, I had to run out and buy sub-par rain gear for the half.
In 2017 for Dopey, the Marathon was basically "Day After Tomorrow" weather. The only warm item of clothing I had with me was my North Face jacket (no Trail Ears, no gloves, no leggings, no funnel-necked top to cover my mouth/throat - NOTHING), so ... again, I took a trip to Uniqlo and
Walmart to buy sub-par items to get me through the race.
I don't do throwaway clothes, because I prefer to be hot over cold - and I like things to be fitted rather than loose/rolling up, etc. - which is a real mental thing more than anything ... I just don't like fussing with things.
For 2018, I'll be damned if I don't have my nice gear for every possible scenario.