+1...
But the Bob probably isn't the cheapest way to go. It will be more than 3 times as much as 2 inexpensive panniers and a rack. Even if you went for 4 panniers and a front and rear rack you can get by much cheaper than a Bob. So if price is the driving issue, you might rethink that.

Alternately you could get a pair of Nashbar or Performance panniers and a rear rack along the lines of the Blackburn EX-1. Maybe $100, less if you catch a sale (they are frequent). Then strap the empty backpack on top of the load.

BTW if you plan to just do overnight or two night backpack trips, it isn't hard to get down to a little 30 liter or so ultralight pack. I have found that, when using a bivy and not needing a bear canister, I can even get my gear and food for 3 days and 2 nights into my 18 liter pack (it weighs a whopping 10 ounces empty). The 30 liter one will (barely) let me take a one person tent and bear canister (The 30 liter pack weighs 1.5 pounds empty).