I'm an experienced cyclist and and have done numerous supported tours where our tent and stuff was carried. My wife and I are heading out for our first fully self-supported tour soon.
My retirement present to myself is this Trek 520 Grando. (None of my other bikes could take a front rack.)
I think have my panniers set up OK.
My questions:

1. What do folks carry on the flat part of a front rack? This bike came with a gigantic front rack. I have a bag (see photo) I could use for my jacket and wallet and such. Good idea? Or should that space be used for something else?
2. How about the flat top part of the rear rack? My tent maybe?
3. Do folks typically carry their sleeping bags outside their panniers? Is rain a concern? Do you plastic bag it?

I've been riding pretty much all my life, bike commuting, double centuries, and supported tours. But this is a new beast. Thanks for your help.