What way would be the best and easiest way to glue beer bottle caps to a fridge? Would spray adhesive work?

Spray glue would not work reliably because the bottle caps would have to be even all the way around to make contact with the glue. If you were to spray the fridge surface first, then a lot of dirt will be sticking to it too and it is very difficult to clean. I would glue a magnet that you can get cheaply from WalMart to the inside of the cap and then place it on the the fridge. You can even get magnets that have adhesive already applied so all you have to do is stick the cap to it.