Can one open a can or bottle on Shabbos or Yom Tov? If so, what’s the best way? What if someone forgot before Shabbos? What about a box of any food or plastic bag that needs to be ripped opened?
It is not permitted to open a bottle that leaves a ring behind on Shabbos. For a metal cap, this is certainly forbidden, and this can be a full Torah prohibition. The reason for this is that opening the bottle cap for the first time is considered makeh be-patish — by opening the lid, the cap is “formed” by losing the ring beneath it (see Me’or Ha-Shabbos p. 481; Shmiras Shabbos Kehilchasah 9 note 61).
It is permitted, however, to puncture the cap (so that the cap is no longer fitting for use) and then unscrew it (Shmiras Shabbos Kehilchasah 9:17).
Some authorities rule that the same halachah applies for bottles with plastic caps. Others, however, rule that for plastic caps there is no prohibition, because the cap is initially formed without the ring, and was therefore already a “complete utensil” (meaning, already a bottle cap) prior to its being opened (see Tikkunim to Shemiras Shabbos, p. 14; Me’or Ha-Shabbos, loc. cit.; see Binyan Shabbos p. 94).
Concerning drink cans, Rav Shlomo Zalman Auerbach (Minchas Shlomo 2:12) writes that it is permitted to open drink cans on Shabbos, because this is a kilkul for the can (opening it effectively “ruins” the can, which is discarded after opening).
However, Or Le-Zion (1:28) prohibits opening a can in a manner that the ring is completely removed, and Rav Elyashiv is likewise quoted as being stringent on the matter, on account of the prohibition of mechatech (cutting to size).
Even where there are lenient opinions that can possibly be relied on, it is generally better to ensure that all bottles are opened before Shabbos.
A box or bag can be torn open on Shabbos, but one must be careful not to tear letters on the packaging. In addition, it is only permitted to open types of boxes/bags that will not be re-used. If one needs to open a can that will possibly be re-used (such as a large can of canned food), one should make a hole in the bottom of the can before opening it.