A: We would rule that any legitimate holiday you can think of should work. No making stuff up…”Yeah, it’s National Elevator Day! That’s the ticket!…” unless it really is National Elevator Day.* You don’t have to specifically celebrate that holiday yourself.
It may be a good idea to apply a house rule about “no looking up today’s date during the game to see what holiday it might be.” I think in our house, we’d probably rule that you could use the internet to verify, but not search for a holiday mid-game. But that would be up to your gaming group.
IN FACT, you could even choose to look up any possible holiday BEFORE the game, so everybody knows (and agrees on) exactly what “special day” it is if that card comes up for them. “Well, we’re about to play Holiday Fluxx, and, just so everybody knows, it happens to be International Day of the Nacho, so, if everybody agrees, that will be what counts for the card Today’s Special!”
Perhaps the most important part of this FAQ is that deciding what is and is not a valid “special day” is something you and your gaming group should agree on BEFORE you start playing. It’s more important that you AGREE than that you be CORRECT about what counts, and that agreement needs to be established before the game starts, not when the card comes up in play.
For example, if you can’t agree what counts as “a holiday” in the broader sense, then you could alternate which way you will play. One game, before you start, agree that you will use one person’s definition/rules. Another game, before you start, agree that you will use another person’s definition/rules.
* There does NOT appear to be a National Elevator Day, but there IS a National Talk in an Elevator Day. It is on the last Friday in July and nobody seems to know where it came from, though you can find it on numerous sites that list silly daily “holidays.”