(Melting ice.)
Other types of necessities (in conjunction with putting frozen liquids and warm areas): child, oneg Shabbos, etc.
חסרון כיס Chesron Kis: A Place Specially Set Aside for This Item or Not?;
opening up knots with one pull;
Does It Have to Be Done for Immediate Use? How Should One Make Salt Water on Shabbos and Yom Tov for the Seder on...