(Melting ice.)
Other types of necessities (in conjunction with putting frozen liquids and warm areas): child, oneg Shabbos, etc.
using magnets and loose leafs on Shabbos;
putting in and taking out a extra piece of the table; removing rust from a utensil; an adult playing with a child Lego, fixing...
Some important details as to when "S'char shabbos" applies.