It is our custom to wear Tallit and Tefillin during the Minha service on Ereb Yom Kippur, and to add the Viduy (confessional) section at the end of the Amida prayer.
The Gemara comments that we recite Viduy at Minha on Ereb Yom Kippur out of the concern that "Shema Titaref Daato" (literally, "lest his mind become confused"). The commentators disagree in explaining the meaning of this remark. Some understand this to mean that a person might become inebriated during the final meal before Yom Kippur, and will thus be unable to properly confess on Yom Kippur. Halacha allows drinking wine during the final meal, and thus the concern arose that one might perhaps drink excessively to the point of intoxication.
The Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), however, explained differently, claiming that a person may fatally choke on his food during the final meal before Yom Kippur. The Sages instituted that one should recite Viduy during Minha, before the final meal, so that if, Heaven forbid, he should choke on his food and pass away before Yom Kippur, he would have at least earned atonement through his Viduy recitation.
Why were the Sages suddenly concerned that one might choke on his food during the final meal before Yom Kippur?
The answer is that the Satan works with extra vigilance before the onset of Yom Kippur. Recognizing the immense power that Yom Kippur has to cleanse us of our sins, the Satan invests great effort to prosecute against us before the holy day, and endeavors to prevent us from experiencing Yom Kippur. There is thus greater concern of risk on Yom Kippur than at other times, and this led the Sages to institute the Viduy recitation at Minha on Ereb Yom Kippur.
Summary: It is customary to wear Tallit and Tefillin during Minha on Ereb Yom Kippur, and to recite the Viduy at the end of the Amida prayer.
