"צביעה באוכלים" (coloring in foods) - the stringent view of some poskim
Does It Have to Be Done for Immediate Use? How Should One Make Salt Water on Shabbos and Yom Tov for the Seder on...
understanding the concept of גזרה שמא יתקע (a person might come to tighten it);
הכנה ליום אחר (Preparations for Weekday): Understanding What It's All About;