An invention nobody really knows about is the invention of fast food. The Romans were the first to have the food on the move idea. With the idea of soldiers and them having to eat, a convenient burger was a good idea to be able to feed the army.
Another invention that no one really knows the Romans invented was advertising and trademarks. Traders would advertise their wares with billboards and signs. Potters would often stamp their name on the pot, as to market themselves for more business.