What is allowed in terms of opening new packages of food on Shabbat, like beigele or chips, or cans of pickles or tuna? What about napkins or tissues that have not been opened and are needed? Can the wrapping be torn? There are food items like chocolates which it seems almost impossible not to tear letters. What to do? Is there a difference between the sanctity of the Hebrew and English letters? If you have run out of cut toilet paper or tissues, can toilet paper be torn? How? When opening a can of tuna, can you drain the water out, or is that borer?
You have asked a lot of important questions from a few different areas of the laws of Shabbat. Since sometimes doing the wrong thing on Shabbat can be a desecration of Shabbat It is for this reason the Mishna Brura wrote in his introduction to the laws of Shabbat that it is incumbent upon us to be fluent in the laws of Shabbat. I will follow in my answer following the rulings of Shmirat Shabbat Kehilchata. In general it is suggested that all food cans and packages be opened before Shabbat to avoid any Shabbat problems. If this was not done, according to some opinions you may not open a can on Shabbat or other packages and juice or milk cartons which by opening them then become a receptacle. On the other hand, there are more lenient opinions which state that if the can or package once opened will be discarded and they were opened in a manner where the opening can't be properly used it is permissible. Even according to the more stringent opinion, if the can, carton, or package were to be opened in a way in which they will not be reusable once opened (for example by making a hole in the bottom first), it is permissible to do so. As far as the tearing of letters, they may not be torn on Shabbat because of the Mlacha of erasing on Shabbat. There is no difference between Hebrew or English letters since this is not an issue of sanctity. (However, Sephardi poskim as Rav Ovadia Yosef Shlit'a and Rav Ben tzion Abba Shaul zt"l are lenient as far as letter tearing if the intention is not to erase.) As far as toilet paper, the melacha of "Mechatech" is involved which is cutting something to a particular size. If one does not have toilet paper ready for Shabbat it may be torn with a "shinui" that is in a way in which normally he would not do so. Such as holding the paper with one elbow and tearing with the other elbow. On Shabbat the tuna should be taken out of the oil and not the oil from the tuna because of the "borer" issue. I hope I have answered all your questions. Using a book which has all the details is strongly suggested. May Hashem assist us in keeping Shabbat properly.