Yes, they were "appropriate" PJ's.... meaning, if they normally sleep in just their underwear, DO NOT send them in just their undies! Give them a set of actual pajama's to wear, if they don't have sweatpants and a loose Tshirt or something else that would work as a substitute.
It isn't an actual "holiday", but just a fun day for the kids since it is the last day before the break and usually they aren't doing much actual work, just parties and movies, games, crafts, etc.
My kids always liked PJ day. :) They can wear their bathrobe for a coat if they want to also.
For juice, I would sent caprisun or something like that.... or just the mini (8 oz) water bottles. It doesn't HAVE to be juice. Water is fine, and probably preferred by a lot of parents and teachers as well.
Snacks? Most schools require them to be prepackaged in some way these days (i.e., store bought), but if it is a private school they may have different standards. A bag of chips or pretzels, washed seedless grapes, crackers and cheese, popcorn.... things like that would be great, in my opinion. I'm sure there will be plenty of cupcakes and cookies already.