This is a quick way to protect your gear (Fuji's X100/s/t) against dust and possible splashes of water (just mind it's not waterproof!)
I think photos will explain everything ;)
I assume you have a lens hood AND any filter (UV, polarizer/anything) on your camera - filter is very important here as X100 series has one major "sealing" flaw: there is a gap on the front of the lens, through which small particles like sand, dust or water can penetrate camera.
Take off the lens hood and put your camera inside any plastic transparent bag.
Now try to attach lens hood back to your camera. It may be difficult if your bag is too thick - try thinner ;)
Grab a knife and carefully cut out part of the bag covering the lens.
Voila! You're done ;) When I was shooting ColorRun I taped the bottom of the bag, so it was quite well sealed.