That's a really loaded essay topic.
Ummm you probably get to live longer
you probably aren't fat and there for less ugly
you cant argue that you spend less or more money cause of the different habbits people have.
I can put it down to potentially live longer, and better looking.
A subcategories of better looking could be...
more sex (but this could give you aids)
better job opportunities (hopefully not with much stress)
better chance of reproducing and having good looking offspring carrying on your genetic line and therefor increasing your genetic fitness.
Id probably just focus on increasing your genetic fitness. There is actually a lot of information available on that... and you can probably write a nice introductory paragraph that sounds like you are writing about the benefits of healthy living.
Good luck with that.