It is permitted to engage in acts of a mitzvah before praying, for those are not one’s personal wishes, but rather the desires of Heaven. For example, on Friday, if after the prayer service there may not be enough food left in the store for Shabbat, it is permissible to buy food before praying (Mishnah Berurah 250:1; Kaf HaChaim 89:25). However, it is forbidden to buy even one item if it is not for the purpose of a mitzvah. If there is no food in one’s house to give to his children who are leaving for school, he is permitted to buy the necessary foods before prayer, since that too, is considered an act performed for the sake of a mitzvah.
Minor activities are not considered to be work, nor a fulfillment of one’s own desires, and they are therefore permissible before prayer. For example, a person is permitted to make his bed before praying, and he is permitted to take the garbage from his house to the public garbage bin. Similarly, he is permitted to read the newspaper a bit and do a little exercise before prayer.
Before praying, it is permissible to put laundry that is already sorted into the machine and turn it on, since this is considered a minor act. However, it is prohibited to sort the laundry and then put it into the machine (Halichot Shlomo 2:5).
It is forbidden to cook and bake before the prayer service; however, a person is allowed to ignite the fire under a pot that was prepared the day before, or to put into the oven a pan that contains food that was previously prepared.
It is permissible in a time of need to dress children or to make them a sandwich before they leave for school, since this is a minor act and it also possesses an aspect of a mitzvah.
It is permissible to compose innovative Torah insights, either by hand or on the computer, before the prayer service. However, it is forbidden to write secular ideas.