The best modification you can get for your bike is your own education. Track schools are, IMO, optimal but pricey. The next best is MSF courses which are usually not that pricey and can lower insurance rates.
After that ensuring you have good quality gear is next on the list. For me other mods should be by necessity or to lower overall costs. For instance, I put on flush mounted blinkers. Not for looks, but on my first bike, the stalk-style always got bumped and popped off, causing me frustration and sometimes money.
Oh, there is one exception that I can think of. If your bike doesn't have frame sliders these should be FIRST (excepting gear and perhaps education).
Dragging knee is for the track, and dragging tail is for the lot. --Kane Friesen
When you're in a car, you're watching a movie; when you're on a bike, you're in the movie. --Robert Pirsig
Identity theft is not Fun