I use a cargo net to hold multiple things/odd-shaped together on a rack. Then I run a nylon strap around the whole thing to hold it fast. Never lost anything yet.

I run 2 panniers, and I can get my 30 degree bag and Neoair mat in them with the kitchen and clothes. I roll my tent and put it on a front rack, with the groundsheet rolled separately at the front of the stuffbag and available to grab and cover up with to ride out a quick thunderstorm