The backpack on wheels became a great and useful invention for many children trying to lug several large textbooks to school at a time. The backpack was turned into a type of rolling suitcase with a retractable handle for pulling when necessary. At times when you are trying to get through crowded halls and have already dropped off your books, pick it up and put it on your back. To make other similar inventions on your own, experiment on what else could be placed on wheels. Your gym bag or mom's grocery bags are two great options that often get very heavy.
There are limited comforts for kids in cars. Once you are finally old enough and tall enough to sit in the front seat, the sun visor is often still too short for your convenience. Invent a sun visor clip-on modification that extends the shade down just a bit farther to shield the sun from your eyes as well. It could be made with something as simple as cardboard and velcro. Make it quickly removable and not so long that the driver has a difficult time seeing past it.
Bring back the old x-ray vision glasses that used to come with many super hero comic books. Glue a feather between two pieces of cardboard and cut these into the shape of glasses lenses. Poke a hole through the center of each for each eye, and glue the "lenses" to a piece of wire that will act as the glasses frames. When you put these on and look at someone's skin, it will appear that you are seeing his bones because of the feather's texture.