Things We Should’ve Had Long Ago

Some things rightfully take time to invent:

Rocket ships. Nonstick frying pans. Pez dispensers.

But some ideas are so simple and obvious that it’s kind of astounding that it took so long for them to be invented.

My list of those inventions includes:

Sticker adhesive on stampsWheels on suitcasesGrids on the back of wrapping paperAlarms on refrigerator doorsApple’s allowing customers to choose their own hold musicSelf adhesive envelopes

Anything to add to the list?