I guess I was spoiled by my old '81 Yamaha because it has a useful helmet lock and a luggage rack I could bungee stuff to. The Ninja has a tiny space under the seat, but you can't put stuff there because it will jam up the seat lock assembly and you'll bend your key trying to unlock it. Go ahead, ask me how I know. :( Also, the helmet locks are useless for my helmet because they are right next to the hot exhaust pipes... my helmet would melt even if my strap were long enough to reach, which it's not. Not to mention, someone could cut the helmet strap anyway.
So, to address these problems, I had my personal seamstress (ok, well, Lemontree) break out her sewing machine. First, to help me carry things like pizzas (yes, every once in a while I will get a pizza on my way home from work), she made a seat strap out of this vinyl fake-leather stuff. It attaches to itself with velcro, making a loop under the seat:
Next, I got a cheap bicycle cable that I can loop through the face shield opening of my helmet and attach to the helmet lock. While the primary reason was to address the useless location of the helmet lock, it also makes it more difficult to steal the helmet (as a knife isn't going to cut a 1/4" steel cable, unless you have some kind of super-knife I've never seen before).
You can see the lock that Kawasaki put on the bike at the very bottom of the picture, which is about 2" above the hot melty exhaust pipe.
Now I just needed a place to carry the cable and a couple of bungee cords. As you know, I'm online a lot and I found a discussion forum where someone had, very cleverly, used a $12 car trash container as a motorcycle tailbag. It's the kind that hangs on the back of a front car seat with a strap -- this chap had used the strap to go under his motorcycle seat, and then tucked the back end into the grab bar (that's the sticky-uppy part behind the seat). $12 is about 1/5th the cost of the least expensive motorcycle-specific tailbag I've found, and you know I'm cheap, so off to K-Mart we went. However, once there, I discovered something even better. See, the $12 tailbag sits on the seat, which would interfere with my pizza-carrying desires. Fortunately, I found a $5 glove box organizer (hey, $7 saved!) that could instead mount behind the seat, leaving the entire seat available for pizza duty.
Lemontree fired up the sewing machine again and added two small straps, which I poked holes in and secured to the bike using the fairing screws:
Here's what it looks like loaded up:
And finally, all closed up:
I still need to do something about the useless mirrors, though. Mirror extenders are available but cost waaay to much, so I'll have to see what kind of cheap solution I can find.