Regarding galley & magnets; no, it's not the type which you can use magnets on. On the inside of the cabinet (on the right) there is a bit of available surface (it protects the back of the 120 and 12v plugs); and I do have a few magnetic things there--they stick well while traveling. Of course, if they happen to fall off it's no big deal. Nothing breakable anyway. I did briefly toy with the idea of placing a steel strip "somewhere" in the galley, just so I could have magnets; but after a year without magnets; I noticed I didn't need that kind of thing anyway. But everyone is different.
But really there is simply so much storage in the galley I simply haven't had a need to use the walls / magnets on the walls.
Stickers... well, personally I would never put stickers on anything, anywhere. I've never cared for any kind of bumper sticker, or stickers period. So I'm not exactly an unbiased opinion on sticker placement. But... if I were to WANT to put stickers on something...how about--the curtains? either the side facing you (interior); or the side facing the window (for display). Otherwise, I'd probably work out some interesting method using 3M strips, the Velcro ones perhaps? 1 end on the back of the sticker (never take off the protective layer) and the other attached to wherever in the galley? that way you can remove or reorganize to your hearts content. I could see (in my mind's eye) using the 3m Velcro + whatever it is you want to display, and make groupings between the hatch ribs/ceiling when you have the hatch open?
But if your goal is that when you are in transit or gone from your site and you want people to see the stickers (i.e., hatch is closed), I'd try to rig something up for the back of the curtains--protected, but yet still visible. And if at some point in the future you find it annoying--it's curtains. Worst case is you make new ones (or buy new ones if you aren't handy with a sewing machine).)