2 hole L brackets and 1″ self tapping screws. The Home Depot special.
 
Pretty much all commercial refrigerators have a inch or two of phone insulation so poking a hole won’t hurt it. Other equipment, just poke around inside where you plan on attaching the bracket and make sure nothing is in the way.
 
Stainless counters, more 1″ self tapping. Go from the bottom and pop a couple through the lip against the wall.
 
I use A LOT of 1″ self tapping screws.