Q. I read that you can’t prepare on the 1st day of Yom Tov for the second, but something insignificant like taking a challah out of the freezer a few hours before the second day starts would be okay. Other sources say things like “Even something that is not actual labor, such as to bring in water, or even wine for kiddush or havdala, may not be done on the first day of yom tov for the second day”. So I’m confused.
1. Is there a general guideline to follow for what would be considered insignificant enough to be allowed to be done to prepare for 2nd day.

2. A specific case that happened on Shavuot: Someone wanted to know if they could bring a cheesecake on 1st day of Yom Tov from one persons house to another persons house, even though they knew that they would be serving that cake only on 2nd day. (she was already going over to that house on 1st day, so it was more convenient to bring it over then, but refrained from doing so in order not to violate the idea of “preparing for 2nd day”……..was that a necessary stringency?).

A. Hachana is the prohibition of preparing from Shabbos or Yom Tov to a weekday or to another Shabbos or Yom Tov day, even if it is a minor provision that involves only verbal instructions (Mishna Berura 503: 1, 116: 2).
However one may prepare for another day if the act benefits the present day also, such as taking out challah from the freezer or wine from the cellar, if there is a chance that it could be still used on the present day.
Horav Shlomo Miller’s Shlit’a opinion is that in the case of the cheesecake, if a small tasting piece is consumed still on that first day at the destination, it is permitted to bring.
The Rov also quoted Chayei Adam (H. Hoshana Rabba and Simchas Torah 157: 6) that there is no Hachana prohibition on bringing items to another house, when in need. The Rov explained that the melacha of Hotza’a involved, is considered a lesser melacha.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a