Q. Is it permitted to quickly buy a few seforim prior to davening Shacharis, such as in a yeshiva where seforim are for sale and one is concerned that if he davens first, someone else will take the seforim that he wants?
A. Poskim permit performing simple, and uncomplicated temporary activities before davening, such as making one’s bed (Pe’eir Hador 2: 213, quoting Chazon Ish and Ribabos Efraim 1: 62), placing clothing into a washing machine or taking out the garbage (Halichos Shlomo 2: 5). See also question 1019 and 2130 in regard to simple exercises, weighing oneself on a scale and other personal body needs are, such as taking a shower, brushing teeth etc. that Horav Shlomo Miller Shlit’a permits before Tefila.
Poskim also permit activities that are mitzvos and Heavenly needs, when they cannot be done after davening, such as buying and preparing the food for Shabbos (Mishna Berura 250: 1), making ready and sending children to yeshiva, (Piskei Teshuvos 89: 15), or collecting tzedaka for the needy or Torah institutions (Aruch Hashulchan 89: 22 and others).
Therefore, the acquisition of a few seforim that may not be available after davening, if kept simple and fast, should be permitted.
Horav Shlomo Miller’s Shlit’a opinion is that it is permitted.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a