Kiddush clubs and the Simchas Torah communal Kiddush-The laws & restrictions in eating before Musaf:
It is permitted to eat after the prayer of Shacharis, prior to the prayer of Musaf, all the foods that are permitted to be eaten prior to Mincha once its time has arrived. Thus, one may eat fruits [and consume non-alcoholic beverages] of unlimited quantity, in order to satiate the heart. One may eat up to a Kibeitza [55 grams] of bread, but not more.
May one eat more than Kebeitza of Mezonos before Musaf?
This matter follows the same law as eating Mezonos before Mincha, which seemingly follows the same law as the requirement to eat in a Sukkah, of which we rule that one is required to eat more than a Kebeitza of Mezonos in the Sukkah. Thus, it is be forbidden to eat more than a Kebeitza of Mezonos prior to Mincha, and the same applies prior to Musaf.
May one drink alcohol before Musaf?
One may drink up until a Kebeitza [55cc] of alcohol before Mincha, and the same applies before Musaf.
Having a Kiddush on Simchas Torah between Shacharis and Musaf:
It is customary to hold a Kiddush on Simchas Torah between Shacharis and Musaf, prior to the start of Hakafos.
Eating and drinking limitations: Although in general it is forbidden to eat more than a Kebeitza of Hamotzi, Mezonos, or alcohol, prior to Musaf, nevertheless, it is permitted for one who is by a communal Kiddush on Simchas Torah, or is at home but plans on joining the set community Minyan for Musaf, to drink wine, and other alcoholic beverages, as well as wash on Hamotzi and eat even more than a Kebeitza of bread or Mezonos during this meal. However, one who is Davening in private, may only eat a Kebeitza or more of bread or Mezonos or alcohol if he has a Shomer to remind him to Daven Musaf.
 Admur 286:4; Michaber 286:3; Brachos 28b
 Admur ibid; See Michaber ibid that “It is permitted to taste”
 Admur ibid
 Admur ibid; Michaber ibid
 M”B 233:35 regarding Mincha
 Admur ibid; M”B 286:8
 Admur ibid as explained in 232:3; Michaber ibid “A small amount of bread even if it satiates the heart, although not an actual meal” Michaber 232:3 regarding Mincha that “one may eat up until a Kibeitza of bread which is considered a snack”; M”A 233:17 regarding Mincha and 286:2 regarding Musaf that one may not eat more than a Kebeitza
 Admur ibid
Other definitions: Some Poskim rule that this follows the same law as eating in a Sukkah. [Shaar Hatziyon 286:7]
 See M”A 233:17 who compares the prohibition to Sukkos, and is even more stringent by Mincha, and the same would apply to Musaf; Shaar Hatziyon 286:7-8 that the Poskim did not define the definition of a temporary meal of Mezonos and that practically we would apply the same law as that which is ruled regarding Sukkos
Opinion of Admur: Although Admur does not explicitly state that it is forbidden to eat more than a Kebeitza of Mezonos prior to Musaf, and simply writes not to eat more than a Kebeitza of bread, one cannot derive from this that it is indeed permitted to do so in his opinion, as a) the term Pas is not exclusive to Hamotzi, as we find regarding Pas Haba Bekisnin; b) Also the Michaber in 232:3 regarding Mincha only prohibits more than a Kebeitza of bread, and nonetheless, the Achronim write that also Mezonos is forbidden and make no inference from this wording that it is exclusive to Hamotzi. c) If this were correct then why would Admur need to mention an allowance of eating fruits, if he could have mentioned an even greater allowance of Mezonos. This is unlike the understanding of Rav Levin in Hearos Ubiurim Ohalei Torah 1043 p. 44 who desires to learn in Admur that before Micnha and Musaf, only Hamotzi is forbidden.
 Admur 639:11 M”A 639:6; Elya Raba 639:12; Levushei Serud 639; Ginas Veradim O.C. 4:6 regarding Pas Habah Bekisnin that the Shiur is more than a Kibeitza; Michaber 639:2 and Tur 639:2 regarding Kevius Seuda on Mezonos products; Shaareiy Teshuvah 639:5 in name of Ginas Veradim to eat more than a Kibeitza of Mezonos in a Sukkah, but without a blessing; See M”B 639:15; Kaf Hachaim 639:39 [concludes to be stringent]; Piskeiy Teshuvos 639:8
Other opinions: Some Poskim rule that one is only obligated to eat Mezonos products in a Sukkah if he sets a meal over them. [Michaber 639:2; Tur 639:2; See Chaim Sheal 1:71-1; Machazik Bracha 639:5; Bigdei Yesha 639; Mamar Mordechai 639:3; M”B 639:13; Kaf Hachbaim 639:39-40] Thus, he may even eat more than a Kibeitza of Mezonos outside of the Sukkah so long as he does not set a meal over it. [M”B 639:15] Some Poskim rule that this applies even by Pas Haba Bekisnin. [Chaim Sheal 1:71-1; Machazik Bracha 639:5; Shaareiy Teshuvah 639:5; See Kaf Hachaim 639:33] If one eats together with a group, then it is considered to be like one set a meal over it. [M”B 639:15; Shaar Hatziyon 639:35 in name of Bigdei Yesha; Kaf Hachaim 639:39] See Kaf Hachaim 639:40 for the exact definition of Kevius and how much one needs to eat; Other Poskim rule that Shabbos and Yom Tov is an exception to the rule of more than a Kibeitza, and that if one ate a Kibeitza of Mezonos after kiddush on Shabbos or Yom Tov then it must be eaten in the Sukkah with a blessing. [Shaareiy Teshuvah ibid; See M”B 639:16 and Kaf Hachaim 639:33]
Shabbos and Yom Tov: Some Poskim rule that on Shabbos and Yom Tov one is required to eat even a temporary meal in a Sukkah, which is from a Kezayis and above of Hamotzi or Mezonos. [See Poskim in previous footnotes, and Piskeiy Teshuvos 639:8 footnote 34] Practically, we do not rule like this opinion. [Setimas Haposkim, and Admur]
 Misgeres Hashulchan on Kitzur SHU”A 69:2 regarding baked Mezonos, based on Shaareiy Teshuvah 639 regarding Sukkah; Kitzur SHU”A ibid that one should be stringent even regarding non-baked Mezonos; See Piskeiy Teshuvos 232:5
Other opinions: Some Poskim rule that it is permitted to eat more than Kebeitza of Mezonos prior to Mincha. [Aruch Hashulchan 639:18]
Non-baked Mezonos: Some Poskim rule one may eat even more than a Kibeitza of non-baked Mezonos prior to Mincha [M”B 232:34; Derech Hachaim7] and outside of a Sukkah [M”B 639:15], so long as he does not eat an amount for which one generally sets a meal on, and in their opinion the same would apply to Musaf. [See M”B 286:8 and Shaar Hatziyon 286:7; Piskeiy Teshuvos 286:8 footnote 60] However, according to Admur, it is forbidden to eat more than a Kebeitza of any Mezonos outside a Sukkah, and seemingly the same would apply prior to Mincha and Musaf, as stated above.
 Piskeiy Teshuvos 286:8 footnote 62 regarding Musaf; We also find regarding similar Halachos that one may not eat more than a Kibeitza of Mezonos: See P”M 431 A”A 4 regarding Bedikas Chameitz, recorded also in Mishna Berurah 431:6.
 M”A 233:17
 Admur ibid that the same laws apply regarding Musaf
 See Piskeiy Teshuvos 286:8
 Admur 286:4
 So rule regarding Mincha, and the same would apply to Musaf, as rules Admur ibid: Misgeres Hashulchan on Kitzur SHU”A 69:2 regarding baked Mezonos, based on Shaareiy Teshuvah 639 regarding Sukkah; Kitzur SHU”A ibid that one should be stringent even regarding non-baked Mezonos; Piskeiy Teshuvos ibid
 M”A 233:17 regarding Mincha, and the same would apply to Musaf, as rules Admur ibid
 See Chasam Sofer O.C. 69; SSH”K 52 footnote 50 and 55 in name of Rav SZ”A; Piskeiy Teshuvos 286:8 footnote 62