Blessings, Kiddush and Birchas Hamazon for one who eats on Yom Kippur:
Kiddush and Lechem Mishneh: One who is required to eat on Yom Kippur due to medical reasons, does not need to say Kiddush, and is not required to recite Hamotzi on two loaves of bread. [This applies even if Yom Kippur falls on Shabbos.]
Blessings: One who is required to eat on Yom Kippur due to medical reasons is required to say a blessing before and after eating the foods.
Yaleh Veyavo in Birchas Hamazon: One who eats a Kezayis of bread on Yom Kippur, is to recite Birchas Hamazon. In Birchas Hamazon, one is to add Yaleh Veyavo prior to Uvinei Yerushalayim and say “Beyom Hakippurim Hazeh”. [However, some Poskim rule that based on Admur in the Siddur one is not to recite Yaleh Veyavo in Birchas Hamazon. Practically it is to be recited.] When Yom Kippur falls on Shabbos he is to also add Ritzei.
If one eats bread on Yom Kippur, is he to wash hands?
Yes, the hands are to be washed up until the wrists as is normally done during the year.
If one who ate bread forgot to recite Yaleh Veyavo in Birchas Hamazon, must he repeat the Bentching?
No. He does not repeat Birchas Hamazon.
Is one to mention Yom Kippur in Al Hamichyah?
 Admur 618/18; M”A 618/10; Shaar Hatziyon 618/22; Alef Hamagen 618/18; Har Tzevi 1/155; Piskeiy Teshuvos 618/15
Other opinions regarding Lechem Mishneh: Some Poskim rule Hamotzi is to be recited over Lechem Mishneh. [Mor Uketzia 618; Kaf Hachaim 618/60; Meishiv Davar 1/359; Piskeiy Teshuvos 618/15] The above Poskim negate this matter.
 The reason: As these matters were not established by the Sages on Yom Kippur. [Admur ibid]
 Implication of wording of Admur ibid that this includes even Shabbos; So rules also Poskim brought in Shaar Hatziyon 618/22; Alef Hamagen 618/18; Har Tzevi 1/155; Piskeiy Teshuvos 618/15
Other opinions regarding Kiddush on Shabbos: Some Poskim rule Kiddush is to be recited when Yom Kippur coincides with Shabbos. [Rav Akiva Eiger brought in Shaar Hatziyon 618/22] The above Poskim negate this matter.
 Admur 196/5; 204/15; Seder 7/9; Luach 10/9; M”B 604/46
 Admur 618/18; first opinion in 188/11
Other opinions: Taz 618/10
 Shaar Hakolel 34/9
 Piskeiy Hasiddur 185; See however Hiskashrus who writes it is to be recited in Harachaman, See Nitei Gavriel Bein Hametzarim 66/11
 Levushei Mordechai Tinyana Y.D. 11; Yad Sofer 7; Shevet Halevi 8/139; SSH”K 39/31; Lehoros Nasan 2/42; Shraga Hameir 5/45; Piskeiy Teshuvos 613/2; 618/15
 Kitzur SHU”A 133/18; M”B 618/29
 Siddur Yaavetz
 Shaar Hakolel 34/9