whats the best way to store them until tomorrow?
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I don't know if this is the BEST way, however I've successfully stored fresh squash blossoms for a day in the crisper of my refrigerator in a single layer on a paper towel and they were still really fresh the next day. It's best to use them immediately of course, but I understand that can't always happen. Enjoy!
If the stems are still attached, you might try standing them in a glass of water and covering loosely with a plastic bag and putting them in the fridge. I've done this in a pinch and they stayed pretty fresh.