The Ben Ish Chai (a”h), states that there is a minhag to dip one’s bread in honey or sugar during the Seudah Ha’mafseket, the final meal eaten before Yom Kipur. Ha’Rav Ovadyah Yosef (a”h) notes that even those who follow this minhag must ensure to have salt on the table, as well, and to dip the bread three times in the salt, as is always done, even if one also dips the bread in honey or sugar.
There is a Torah obligation of “Tosefet Yom Ha’kipurim,” (adding a few minutes onto the observance of Yom Kipur). The Torah states that the Yom Kipur observance begins “Be’tisha la’chodesh ba’erev – on the ninth of the month, in the evening” (Vayikra 23:32). This indicates that the fast should begin on the ninth of Tishrei, the day before Yom Kipur. Therefore, we begin the observance of Yom Kipur a few minutes before sundown on Erev Yom Kipur.
One who finishes his Seudah Ha’mafseket and then wishes to eat or drink may do so, provided, of course, that the time to begin the fast has not yet arrived. This applies even if he recited Birkat Hamazon. As long as the time for the fast has not arrived, one may continue eating and drinking despite the fact that he completed the formal meal.