For me it was the refrigerator. It was such a hassle draining the ice box every other day. The blocks of ice which were delivered a couple of times a week didn't last long during the hot summer months. Ice cream didn't last long in the ice box and often melted by the second day.
With the refrigerator I can keep and freeze food in the freezer section, even make my own ice! I don't have to go to the market every day. I can buy a week's worth of groceries now. My refrigerator holds a lot of food.
An then, in the early 70's I bought a microwave oven!