I need a science fair invention! any ideas

I have search tons of things but they aren't what I looking for. I have to invent something or improve on a exsisting object. I only have 3 days to do this, so it would be nice if it was east to make. Its for a 8th grade project

Know what I would want to see??? A pair of sandals, with insoles attached, that still looks cool. I'm in grade 8 too, and I really would love to see that. I have very high arches, so sandals are uncomfy, but I think this could be really awesome.

TickleMe Plants Sprout in 3 days. They are the only plant that move when you tickle them. Show how you invented a way to improve germination by pouring boiling water over the seeds and then plant them.
Set up a control group without the boiling water. Visit www.ticklemeplant.com for more information and to get a science kit to grow your own. I hope this helps

maybe a book mark that can be magnectically attached to the back of the book with a piece of string hanging off that you can use (as normal magnetic ones are annoying to take on and off), or you can rip off the toe part of a toe sock and say its a toe warmer for in the summer when your toes get cold but you dont wanna wear a whole sock.

how about a spell checker?

or an umbrella that doesn't turn inside out in the wind, or a hooded jacket with a hood that doesn't blow back in the wind?