I also got the D80 and 18-135 bundle.
It was an insurance replacement and they gave me a Lowepro Rezo 160 AW. See link.
http://www.lowepro.com/Products/Shou...zo_160_AW.aspx
It's perfect for what you are looking and I use mine in much the same way.
It won't take much more though and I will need a slingbag to take any bigger range of longish lenses