a. Many individually wrapped candies, lollypops, ices, and other "Shabbos Party" type treats have lettering and/or designs just at the spots that you would open them to take out the candy or treat. This constitutes an Issur DeRabbanan of Mochek (Shulchan Aruch, Orach Chayim 340; Mishne Berurah, seif katan 17). We note that this problem is true of "heimishe" products as well, as the manufacturers do not assume that you or your children will necessarily be opening these items on Shabbos. Perhaps we should add to the list of Erev Shabbos things to do--checking packaging of this kind!
b. According to the Sefer HaShabbos BeTifarta by HaRav Avrohom Adas, Shlita, reattaching a broomstick back to a broom either by screwing it back in, or by pushing it with force back into place, constitutes an Issur DíOraysa of Boneh. He likewise rules that one may not return a belt buckle to a belt on Shabbos.
c. Several important Borer points from the Sefer "Pnei Shabbos--Halachos HaSchichos" by HaRav Yosef Glick, Shlita of Yerushalayim, which provides the answers to many common Shabbos Shailos: (i) One may not pour off the liquid from cholent unless he leaves some amount of liquid in the cholent, or eats a little bit of the liquid that he poured off--so that he is selecting the Ochel (that which he now wants) from the Pesoles (that which he does not now want) for immediate use; (ii) When clearing the table, one should make sure that the dirty plates are somewhat separated from the plates with remaining food on them that he wants to put away, in order to avoid the potential borer of separating plates mixed together--removing dirty plates from the table to discard their contents while removing plates with food to store their contents. Likewise, there should be distance kept on kitchen counters between the dirty plates and plates with items to be discarded, and the remaining clean plates, or items to be stored, in order to avoid borer issues of selecting Pesoles from Ochel--or even Ochel from Pesoles for non-immediate use; (iii) One should not remove noodles from chicken noodle soup simply because he does not want to eat them (and vive versa, one may not pour out the chicken soup in order to eat the noodles only), as this constitutes borer--selecting the Pesoles from the Ochel; (iv) One should not remove the frosting or cream layer from a cake, unless he also removes some of the cake along with it, or leaves some of the cream on the cake; (v) If one took a fruit out of a bowl to eat, and then did not like the way it looked, HaRav Shlomo Zalmen Auerbach, Zítl, writes that it may be best to put it back into the same bowl and not somewhere else, so it does not appear as borer; (vi) One is permitted to take the peel off fruits and vegetables immediately prior to consumption--even if the outer layer is inedible (such as a banana peel), because this is deemed to be its "derech achila." If a peel is otherwise commonly eaten, such as an apple peel, there is a Machlokes HaPoskim as to whether one can peel the apple for non-immediate consumption. HaRav Moshe Feinstein, Zítl, forbids it; (vii) If a candy wrapper is stuck to the candy, one should only remove the candy close to its consumption, as the wrapper would then be treated as the peel of a fruit; (viii) If one has different flavors of soda in the pantry mixed up together, and wants to select a few flavors to put into the refrigerator for the Shabbos Seudah in a few hours, there is an issue of borer, as he is selecting for non-immediate use. Accordingly, one should keep the same flavors grouped together so that he is not selecting one flavor from another, or, in the alternative, not be selective about the soda he is taking but simply pick up two or three bottles of whatever may come to his hand. Another alternative may be to immediately drink a little of the soda one selects before putting it in the refrigerator, so that he is selecting the soda for immediate use; (ix) One should avoid peeling corn directly off the cob unless it is close to the meal (even then there may be a separate issue of Dush--although one may eat corn directly from the cob); (x) There are various opinions as to how close to the Seudah one is permitted to peel vegetables, set the table, and perform other Ochel Mitoch Pesoles activities. Although many Poskim rule one has a half-hour before the Seudah, HaRav Moshe Feinstein, Zítl, rules that it is less time than that if one in fact needs less than a half-hour. The situation may also be different if one has many guests, and may depend upon what else has to be done before the meal. One should definitely not rely upon his own "common sense" in this area, which could involve several Issurei DíOraysa within the preparation of one Seudah. Instead, one should most definitely consult with his Rav or Posek in any case of doubt. If one never has any issues or doubts in this delicate area--than he is either being extra-specially superbly careful--or he should immediately commence the study or review of the Halachos of borer, to help himself and others properly observe Shabbos Kodesh!