List of things that are cool to invent:
A machine that crafts you food instantly (ej: You say: Pizza, and the machine makes a pizza, stating the type of pizza you want)

It may sound kiddish, but i prefer travelling on a fictional big boy trough space rather than in a spaceship that looks like a fridge (also ugly)
The translating machine that Ninja said. it would be helpful for books.
Nano robots that can reproduce cells and heal (swats)
Teleporter
The delorean. Time to rob that train.
Space battleship
Dubel toast, sorry.