I've done a few in the past, all the ones I wired were done from the outside with the penetrations done with rigid conduit nipples. Then we would seal the penetrations with silicone AND also fill the nipples with silicone to avoid condensation build up in the equipment.
As far as wiring is concerned I remember light fixtures, condensers, anti-sweats, anti-freeze, alarms (for when the doors are left open), and control wiring that went back and forth between the manages office and the the front of the store that recorded and controlled temperatures, humidity, etc.
Mind you this was all spec and probably over kill for what the NEC would allow.
As for the MC cable being used in the walk-ins, I've had inspectors shoot it down.