Hacham Ovadia Yosef, in his Hazon Ovadia – Laws of Sukkot (p. 115), cites a debate as to whether one may fulfill the obligation to eat bread in the Sukka on the first night of Sukkot by eating bread with a spread or dip. According to one view, the Ke'zayit of bread eaten to fulfill this obligation must be eaten plain, without any spreads and without dipping it in any condiments such as Tehina and the like. Although other authorities allow eating the Ke'zayit of bread with spreads and dips, Hacham Ovadia rules that one should preferably follow the stringent view and eat the Ke'zayit of bread plain. (Of course, after eating a Ke'zayit of plain bread one may then eat bread with spreads and the like.)
The Rama (Rabbi Moshe Isserles, Poland, 1520-1572), in his work Darchei Moshe, cites the ruling of the Maharil (Rabbi Yaakov Halevi Molin, Germany, 1365-1427) forbidding the consumption of bread during the afternoon of Erev Sukkot. This ruling stems from the Halachic association between the obligation to eat bread in the Sukka on the first night of Sukkot and the requirement to eat Masa on the first night of Pesah. Just as Halacha forbids eating during the afternoon of Erev Pesah, to ensure that one eats the Masa with a hearty appetite, it is likewise forbidden on Erev Sukkot to eat after midday, so that the Ke'zayit of bread in the Sukka will be eaten with an appetite. However, Hacham Ovadia Yosef cites numerous authorities, including the Mishna Berura (work by Rabbi Yisrael Kagan, the "Hafetz Haim," Lithuania, 1839-1933), who limit this prohibition to the late afternoon hours of Erev Sukkot. In their view, the prohibition begins at ten hours into the day, which this time of year (in the New York City area) is at approximately 3-3:30 PM. It should be emphasized that this prohibition applies only to bread; it is permissible to eat other foods, even after the tenth hour, provided that one does not fill his stomach completely.
Later in the aforementioned work (p. 122), Hacham Ovadia makes reference to the debate among the Rishonim (Medieval Halachic scholars) as to whether one must eat a Ke'zayit of bread in the Sukka on the first night even when rain falls. The Hacham follows the opinion that one is not required to eat in the Sukka when rain falls on the first night, in light of the famous Halachic principle of "Mista'er Patur Min Ha'Sukka" – one is exempt from the Sukka obligation if residing in the Sukka would cause discomfort. This is in contrast to the ruling of the Rama, who held that one must eat a Ke'zayit of bread in the Sukka on the first night even in inclement weather. Hacham Ovadia notes that even according to this stringent view, one would not recite the Beracha of "Lei'shev Ba'sukka" when he eats in the Sukka in the rain.
In such a case, when rain falls on the first night of Sukkot and one therefore eats indoors, does he recite the Beracha of She'heheyanu the following day, when he eats in the Sukka for the first time?
Hacham Ovadia (ibid. p. 125) cites authorities who indeed require reciting She'heheyanu in such a case given the occasion of eating in the Sukka for the first time. Others, however, disagree, claiming that this Beracha is unnecessary as the individual recited it the previous night to mark the occasion of Yom Tov. Hacham Ovadia employs here the rule of "Safek Berachot Le'hakel" – that one should not recite a Beracha if it is uncertain whether it is required – and therefore She'heheyanu should not be recited in such a case.
Summary: When one fulfills the Torah obligation to eat a Ke'zayit of bread in the Sukka on the first night of Sukkot, he should eat the bread plain, and not with any spreads, condiments and the like. One should refrain from eating bread after the tenth hour of the day on Erev Sukkot. One may eat small quantities of other foods, provided that he will still have an appetite for the meal in the Sukka. If rain falls on the first night of Sukkot, one is not required to eat even a Ke'zayit of bread in the Sukka. When he then eats in the Sukka for the first time the following day, he does not recite She'heheyanu.