Previous:  Those which are meticulous are accustomed to fast for a total of ten days, and so is the proper custom. [However those which feel weak from fasting are not to fast these fasts. Practically the custom today, due to the weakness of the generation, is that we are no longer fast these fasts.]
Pas Yisrael: During the ten days of repentance one should be particular to only eat Pas Yisrael [bread baked by a Jew], even if his custom is to be lenient in eating it throughout the rest of the year. However all the allowances that apply during the year apply likewise during these ten days.
Sparks of Kabala:
Although fasting during Aseres Yimei Teshuvah is an act of piety nevertheless the main Tikkun during these days is actually fulfilled through eating. The fasting is only done due to the requirement to achieve atonement for sin. It is therefore written in Sefarim that one must eat bread every night of Aseres Yimei Teshuvah in order to recite the blessing of Birchas Hamazon.
 Rama 581/2
 See Kaf Hachaim 581/62 that it is not necessary to fast until nightfall, although it is proper to do so.
 See Mateh Efraim 581/36 [brought in Kaf Hachaim 581/61] however there it is with regards to if fasting may cause one to be unable to fast on Yom Kippur.
 603/1; Michaber 603/1; M”B 603/1; Shach Yoreh Deah 112/9; Toras Chatas 75; based on Yerushalmi Shabbos 3/3
Chulin Al Taharas Hakodesh: The Shlah p. 67 [brought in M”A 603/2] writes that Chassidim are accustomed to not eat impure foods, thus they only eat foods that have not touched water and that have been kneaded with fruit juice. The M”A ibid leaves this matter in question being it becomes impure with the saliva in one’s mouth being that we are all Tamei Meisim. Other Poskim defend the ruling of the Shalah [Elya Raba 603/1] Practically this matter is no longer accustomed today. [Kaf Hachaim 603/6]
 Thus even if he cannot bake the bread himself, he can Kasher the oven of the gentile by raising the flame or throwing in a single twig, in which case the bread is no longer considered Pas Palter. [ibid; Michaber Yoreh Deah 112/9] Likewise if one is traveling and has no Jewish bread available for a distance of 4 Mil ahead of him and he now desires to eat, then he may eat Pas Palter even during Aseres Yimei Teshuvah just as it is allowed during the year. [ibid; 112/16; M”A 603; Elya Raba 603/1; M”E 603/1; M”B ibid]
 Ben Ish Chaiy Netzavim 24; Kaf Hachaim 581/60