Many use T-bags that slip over the sissy bar/backrest and secure with straps and hook system if you are looking at "ballistic nylon" type setup. Other use the passenger pillion and a saddle pack the can either slip over the sissy bar/backrest or clip hooks and straps to the seat or grab bar/frame. Either way, as Prof stated, make sure it is secure, when storage is behind you out of sight, you can lose stuff and not be aware until it is too late! :s