When Yom Tob falls on Friday, Halacha forbids preparing on that day for Shabbat unless one made an Erub Tabshilin before Yom Tob. This year (beginning of 5775), we will be observing three sets of Yom Tob on Thursday and Friday (Rosh Hashanah, the first two days of Sukkot, and the two days of Shemini Aseret and Simhat Torah), and thus the requirement of Erub Tabshilin is very relevant this year.
While it is clear that Erub Tabshilin allows food preparations on Yom Tob for Shabbat, it is questionable whether it also permits other preparations. One example would be preparing the Sefer Torah in the synagogue. The reading on Rosh Hashanah is from Parashat Vayera, in the Book of Bereshit, and thus the Gabbai in the synagogue may wish to prepare the scroll on the second day of Rosh Hashanah for the Shabbat reading by rolling it to Parashat Ha’azinu, at the very end of the Torah. Another example is preparing the Mikveh on Friday for those women who will need to immerse on Friday night. Are these preparations allowed through the Erub Tabshilin, or does the Erub Tabshilin cover only cooking, baking and other food-related needs?
The Hida (Rav Haim Yosef David Azulai, 1724-1807), in his Mahazik Beracha, rules that the Erub Tabshilin allows these kinds of preparations only if one made a clear stipulation to this effect when he made the Erub. When reciting the Erub Tabshilin declaration, one must specifically state "U’le’me’ebad Kol Surkana" – that the Erub should permit all needs that must be done for Shabbat, in addition to food preparations. Most other authorities, however, disagree with this ruling, and maintain that even if no explicit stipulation is made, the Erub Tabshilin covers all preparations, and not just those related to food, and this is, in fact, the accepted Halacha.
Summary: When Yom Tob falls on Friday, one may not make preparations on that day for Shabbat unless he makes an Erub Tabshilin before Yom Tob, in which case he may make all preparations that are needed for Shabbat.
