The minhag applies to breads, cakes, pies, pretzels and crackers. (In technical terms, it applies to all pas habo bikosnin. (For an in-depth explanation of pas habo bikosnin, see the following article http://oukosher.org/blog/consumer-kosher/the-mezonos-roll-is-it-a-piece-of-cake/)

Wheat flake cereals are not considered pas. There are differing opin�ions as to whether Cheerios is considered pas. The OU poskim do not consider it pas, because of the size of the individual pieces and the manner in which it is made.

Once the bagel is fully baked by a non-Jew, it can no longer become pas yisroel. Toasting the bagel is not considered a completion of the baking. However, if the bagel was not completely baked (i.e. slightly raw or very light in color) then the completion of the baking by the Yisrael would render the bagel pas yisroel. In the reverse situation, a bagel baked by a Jew is considered pas yisroel once the bagel is edible, even if not fully baked. A pas yisroel bagel does not lose its status even if a non-Jew finishes the baking or toasts the bagel.

Yes. A pie shell fits into the category of pas ha'bah b'kisnin (refer to OUKosher.com article mentioned above for a definition of this term) and therefore should also be pas yisroel. However, if one purchases pie shells that are not fully baked, then they will become pas yisroel when one completes the baking. One should not use non-pas yisroel graham crackers to make their own pie shells.

Yes, bread crumbs should be pas yisroel as well. There were poskim who were lenient regarding bread crumbs that are used for deep fry�ing. This is because frying is a different process than baking and the deep frying is viewed as the completion of the bread crumb prepa�ration (see Teshuvat Avnei Nezer Y.D. 100). Since this is a matter of dispute, unless there is a pressing need, pas yisroel bread crumbs should be used.