The large one I attach to a cheap-o wire hanger with binder clips. The hangers aren't quite wide enough, but come close enough for my purposes. The flag is a little too wide for the depth of the cabinet anyway, so it helps to have the corners curve a bit.
For the garden-sized ones I clip several to one hanger:
Skirt/slacks hangers would of course work well for these and eliminate the need for clips, but that gets expensive when you have a lot of flags!
Over on the far left of the closet I have some of my computer cart covers.
Seasonal Snoopy fabric makes everything more fun!
The wire hanger/binder clip combo is also part of my poster storage, but that's for another post. If you're in need of something to cheer up some wall space, go get yourself a couple of flags!