Taḥanun is not recited on Erev Yom Kippur during Shaḥarit, since the day is a quasi-holiday, and Taḥanun has an element of broken-heartedness that impairs the day’s joy (SA 604:2). Most communities also omit Taḥanun during the Seliḥot recited the preceding night, because the night, too, is somewhat festive. Nevertheless, they do recite vidui in Seliḥot. This is the custom of Ashkenazim, Yemenites, and some Sephardim (Levush 604:2; Shiyarei Knesset Ha-gedola; Shulḥan Gavo’ah; Kaf Ha-ḥayim 604:19). Some Sephardim recite Taḥanun if they are praying before dawn, but not if they are praying after dawn (Ma’amar Mordekhai, Hilkhot Ḥagim 44:4).
Ashkenazim do not recite Avinu Malkeinu on Erev Yom Kippur unless Yom Kippur itself is on Shabbat (when Avinu Malkeinu is not said), in which case Avinu Malkenu is recited at Shaḥarit of Erev Yom Kippur. Sephardim always say Avinu Malkeinu on Erev Yom Kippur, as many of them recite it even when Yom Kippur itself is on Shabbat (SA and Rema 604:2; MB ad loc.; section 7 above).
Eulogies are not delivered on Erev Yom Kippur unless the deceased was a Torah scholar. In such a case, eulogies are offered where body is present (SAH 604:4).
Some communities recite extra Seliḥot on Erev Yom Kippur, while others recite fewer (Rema 604:2). Ashkenazic practice for the past few centuries has been to recite fewer Seliḥot, in accordance with the opinion that there is a mitzva to eat and drink at night as well, which implies that it is a quasi-holiday on which Seliḥot should be kept to a minimum (Shlah). Sephardim do not shorten the Seliḥot, as they are recited at night. Nevertheless, it is good for even those who recite the full Seliḥot to eat and drink a bit extra on the night of the ninth.
Some have the custom of going to mikveh on Erev Yom Kippur, to purify themselves in anticipation of the Day of Judgment and as part of their repentance. However, no berakha is recited prior to this immersion since it is only a custom (SA 606:4). One who wishes to follow this custom but finds it difficult may wash with nine kavim (approximately 11 liters) of water instead (Rema ad loc.). That is, he should stand in the shower while nine kavim of water streams down on him without interruption. He should ensure that this water comes into contact with his entire body (Peninei Halakha: Festivals 1:16 and n. 8). In the past, women immersed before Yom Kippur. Nowadays, very few women do so.
Some had the custom of undergoing thirty-nine lashes after Minḥa, to inspire them to repent. The person being whipped would bend forward, and the person administering the lashes would strike him on the back while reciting the verse “Ve-hu raḥum” (Tehilim 78:38) three times. He would administer one lash with each word. The lashes were not strong. It was done with any type of string or strap and meant to recall the punishment of lashes (SA and Rema 607:6). Nowadays, very few people do this.
Even though the mitzva to confess is primarily on Yom Kippur, our Sages instituted the recitation of vidui before the se’uda ha-mafseket as well. This was out of concern that someone might get drunk during the meal and thus be unable to confess on Yom Kippur itself. Therefore, the custom is to recite Minḥa before the meal and to confess then, during the silent Amida (Yoma 87b; SA 607:1).
At the start of Yom Kippur, before going to synagogue for Ma’ariv, many parents bestow berakhot on their children.