What beauty tool or cosmetic makes the biggest difference?

If you had to name the one thing you could do to change your looks for the better, what would it be?  I hear many women carry mascara as their "must have" cosmetic.  I've always been a lipstick woman, preferably red.  But I've started wondering if there is something else that should be me one go-to thing if I only have a few minutes.  So I've decided to do an experiment.  I start out with a picture of me with hair pulled back, no make-up, no jewelry.  Then I add 1 thing and take a picture, then another day I add 1 different thing and take a picture.  And at the end of it all maybe I'll know which does make the biggest change for the better.
I'm even going to be brave and share my experiment with you.  First off, here's my bare me photo.  Hopefully you can see that my skin is kind of blotchy - lots of red dry spots after this winter, and being a natural blonde, my eyelashes are light so without mascara my eyes don't draw much attention.  I'm not young enough to have perfect, line free skin, but not so old that I no longer break out every month.  So I've got lots that I think I need to cover up or enhance.  Feel free to share your opinions if any of you have tried similar experiments.