I've got a Schwinn seatpost rack, upon which sits a totebag with extra tubes and some tools. I will sometimes bungee a second bag on top of that, and I usually wear a soft Swiss Army attache that has a shoulder strap and two lumbar straps. That thing isn't going anywhere. I wiped out on a descent a few days ago, and while the plastic doo-dad that adjusts one of the straps broke on impact with the pavement, the other two held, and the bag probably cushioned my fall!
I recently changed bikes, from a dept store hardtail MTBSO to a Univega Trail hybrid I found on Craigslist. I believe the new ride can take a bolt-on rack, so I may change my set-up once I save up some cash. Mebbe get some fenders, too.
/F/r/e/d/ Kevin