Yosef Karo

“ Know this: the (minimum) quantity of Pat Shacharit is a k'beitza and afterwards have an [alcoholic] drink if he has one, otherwise water as it says in B"M 107b, bread in salt and a flask of water, and Rashi explains, "if he doesn't have wine." And in Sukkah 26a: a snack may be eaten outside the Sukkah.. like those the students of Rav who taste [something] and enter the lecture, namely like the Rosh and Rashba wrote, "There are seven ways.." ”

“ Know that it's not our custom at all and our rabbis don't have a habit of it, on account that we've heard that Pat Shacharit can only be eaten with produce far from the city, and the time is neither [early as] when the rooster crows nor [late as] when those that tug the boats are heard; whereas those that are accustomed to it would need to eat it at a fixed time every day. ”

“ Three things wear out the body: eating while standing, drinking while standing, and having relations while standing. Chuppat Eliyahu Rabba shaar 3 and it's in at the end of R"Ch ??, and the YP"L #6 brings it and wrote one needs to be most careful about this one, eating Pat Shacharit, see there. ”