Put food out for birds

It's more difficult for birds to find food once the weather turns cold. Happily for anyone who just happens to have leftover food, birds like all sorts of human-ish goodies. The Royal Society for the Protection of Birds recommends leaving out moistened bread, cake, milk, grated cheese, cooked potato, raisins, fruit, pastry, dry oats, black sunflower seeds, and water for the winged in winter. 

Effort involved: pretty negligible. And you get the advantage of something to look at through the window.