I feel like I've almost done it all! It's varied for me from pumping in the car on battery power, pumping in a bathroom stall on battery, to using an incomplete bathroom with the door propped in place (open office, renos weren't finished by the time we moved in!!!), to a completed private bathroom, to a conference room with blinds but no lock, but mostly the office of whichever boss is out that day. Heck, totally OT, but I even pumped at a Six Flags amusement park one day on my 5th wedding anniversary!
My favorite was the private offices. In both they had a free plug in and I'd sit on the floor with my back to the door (or even resting against the door). I just felt weird sitting in my boss's chair at their desk. Second most comfortable was the conference room, but was more worried about people walking in on me there, even with a post-it note on the door.
I just packed things up at the end and stopped off at the washroom or kitchen to rinse/sterilize/store before the next session.