You can also put your clean laundry under your mattress so you don't have to iron - a good way of saving electricty.
Boiled too much water in your kettle? Keep a large flask by the kettle and pour it into that. Use for washing up.
Making a casserole? Get a tea chest or other large box and fill it with hay. Bring the casserole to a rolling boil, pour into a suitable container, and bury in the hay overnight. By lunchtime, it will be cooked.
Driving on a long journey? Wrap your joint of beef and some large potatoes in lots of tin foil, with a bit of oil. Put in a safe place on the car engine. Secure. When you arrive, serve with salad. :)