I've never used bungees since I lost a pack off a rack in Belgium. It had ID in it and the police eventually got it back to me. Bungees can allow things to bounce and move a bit. A good tight strap with one of those roller buckles is the thing. If you're strapping the compression sack right on the rack, it's best to put something between it and the rack. I use rubber stair tread material zip-tied to the rack, but foam, a pad, anything like that will work. You don't want to rub the paint off the rack or wear through the coating on the compression sack.