Q. Is one obligated to eat only pas yisroel (bread baked in a Jewish bakery; as opposed to kosher bread baked anywhere) during the aseres yemei teshuvah? What happens when someone must travel?

A. Shulchan Aruch (O.H. 603: 1) rules that during the Asseres Yemei Teshuvah, due to the unique status of these days, and to beseech Hashem to judge us with rachamin and compassion, everyone should be careful to eat only pas yisroel. From the wording of the Shulchan Aruch and Mishnah Berurah (ibid. 1), it seems that it is a requirement. Nachalas Shivah (72) also mentions that is an obligation. However, Chayei Adam 143:1 and Aruch Ha-Shulchan, maintain that it is only the correct thing to do.
When no pas yisroel available, Shulchan Aruch (112: 8) quotes different opinions if one is allowed to eat pas paltar. Mishna Berura (ibid.) rules that If pas yisroel is available within a “mechalech mil” (a walk or in our days a drive of about 18 minutes from one’s home), one should drive there and purchase it. If pas yisrael is not available within that distance, one should bake his own bread or assist a non-Jew in the baking process. If one is on the road, he should travel ahead another four milin or 72 minutes in order to obtain pas yisrael. If pas yisrael is not available within those distances and one cannot bake his own bread, then he may eat pas palter See Chochmas Adam 65:4; Pischei Teshuvah Y.D. 112:; Mishnah Berurah 603:1; Beiur Halachah 163:1; Aruch ha-Shulchan Y.D. 112:18.
Horav Shlomo Miller’s Shlit’a opinion is that it is only the correct thing to do.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a