If you wish you could have invented something what would it be and why?

I have most of it done, but I wish I could have invented the cell phone case that converts radiation from the phone and turns it back into electricity.

There's also another one which is a watch/ wristband that changes color depending on the loudness of the user's speech. To be used by deaf people.

I wish I could've/could invent food with nutrients but no calories. That way girls (and guys, for that matter) around the world could purchase this INEXPENSIVE delicacy (I'd MAKE SURE it was CHEAP!) and lose weight without starving.