I got one of those "spider web" bungee deals.....15" x 15"........(stretches to 24" x 24".....just clip it over the passenger seat, onto the rack below.......Keep my crap in my "pilot bag"....soft nylon bag.........and put that under the spider web deal......
Really stays put, when I get to work I just remove the bag and bring with me.........
Cookie
I did that for awhile. Eventually, it just got to be a PITA to strap and unstrap my stuff all the time. Plus, I started to scratch up my rear plastics. I eventually picked up a set of cortech/tourmaster saddlebags on craigslist for $60. Loved em. Loading/unloading was so much easier. Eventually picked up a tankbag from my neighbor after he got a new bike with a non-metal tank top. I took the saddlebags off when I was replaced the muffler and did a fenderectomy and really haven't needed to put them back on, since the tank bag holds all I need for a regular trip to work or around town.