The Poskim discuss whether one may open a soda can on Shabbat. This Halacha is contingent on Maran ruling (314:1) that it is prohibited to make a "nice opening" in a vessel. Doing so is considered "Metaken Manah"-fixing a vessel. One may might assume that puncturing the opening of the can also forms a nice, smooth opening, and should therefore be prohibited. Nevertheless, the Poskim, including Hacham Ovadia and Rav Shlomo Zalman Auerbach (Jerusalem, 1910-1995), say that Maran was only referring to vessels which will be used repeatedly in the future. When opening a soda can, one merely wants to remove the liquid, and has no intention of fixing the vessel for further use. Therefore, it is permitted to open a soda can, and there is no problem of "Metaken Manah."
The Menuhat Ahaba (Rabbi Moshe Halevy, Israel, 1961-2001) writes a Chidush that it is problematic to drink directly from the can, because it is considered that the vessel itself was fixed and rendered a temporary cup. Hacham Ovadia (Hazon Ovadia, Vol. 5, p. 384) rejects this approach and permits drinking directly. Rav Shlomo Zalman was also lenient on this issue.
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The Poskim also discuss whether it is permitted to separate yogurt cups that are attached together. The Menuhat Ahaba, is strict, basing himself on Rambam, whereas Hacham Ovadia and Rav Shlomo Zalman are lenient. Hacham Ovadia (Halichot Olam 4:254) argues that each cup is distinct and is designed to be separated; thus, there is no similarity to the case of Rambam. Hacham Bension is also lenient (Or Lesion 27:7) comparing this case to the Gemara's case of "Hotlot Shel Temarim"- a reed basket, which may be ripped open. This flimsy type of packaging is considered nothing more than a shell which wraps the nut.
Similarly, it is permitted to rip open a potato chip bag and the like. It would also be permitted to separate tea bags which are attached to each other. There is no violation of "Mehatech" (ripping) because there is no intent to rip according to a specific measure, and therefore that prohibition does not apply. However, there may be an issue of the Melacha of Koreah, and therefore, some Poskim say that it should be ripped with a Shinui (unusual method).
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There is an issue of opening a bottle which has a cap attached by a ring. When the cap is twisted, the ring separates and falls to the neck of the bottle. This may constitute a violation of Shabbat, since the act of twisting the cap now enables the cap to function as such. Before, it was a seal of the bottle, and now it is a separate vessel. Rav Shlomo Zalman distinguishes between metal and plastic bottle tops. The metal caps have a ring which is an integral part of it, attached by perforation. Twisting it open creates a new entity. The plastic ones are not a part of the cap itself, and do not constitute a problem. Some Poskim, such as the Menuhat Ahaba, say that neither variety is problematic, since it was always considered a cap. However, he rules that it should not be used to cover a different bottle, since that is already a new function.
SUMMARY
It is permissible to open a soda can on Shabbat and drink from it.
It is permissible to separate attached yogurt cups and freeze pops.
It is permissible to open bottle tops attached with a ring, although it is recommended to open them before Shabbat, especially the metal type.
