My bike doesn't have rack eyelets and I'm using it for a 16 mile (each way) daily commute, so I was looking for a Carradice-style setup that didn't cost a hundred bucks.

I got the bag at a thrift store for $3 - I only need enough space for my lunch and maybe a few items of clothing (I keep everything else at work), so it was a perfect size. Only modification I made was to shorten the straps.

For the rack itself I used a Kryptonite U-lock mount for the base, and bought a length of aluminum from Home Depot for about $4 that I cut up. It looks a bit rough, but I haven't had any issues (bouncing around, leg contact, etc) in the past three days of commuting.