Mine was a reverse experience. I was called out to do perform a software update at a customer's test setup. This was a 5 hour drive through a cold winter afternoon, and I arrived close to 5pm. We were going to test the next day, so I planned on doing the update in the evening to be ready the next day.
Everybody left the building at 5pm (this was Germany), but they left me with an access badge to the equipment room (no bigger than a broom closet, and it was nicknamed 'the submarine' for the cramped space), and told me to just park all my stuff with me, as the offices would be closed.
Anyways, at around 9pm I decided to go for a coffee and left the room. It was only when I got back when I realised my access badge was only valid until 8pm.
The security guard left in the building didn't have access to this particular room and didn't offer much of any help.
So now I'm outside the room, where inside are my car keys, my wallet, my phones (yeah, stupid), my laptop bag and my warm coat.
I did mention it was winter. It was well below freezing, it was snowing and I was only wearing a polo, and I was far away from my hotel, and taxis require money.
I ended up walking 1km up the hill from the building, to get to a local hotel*, where the owners trusted a talking popsicle with a room, with a promise to pay next day.
Needless to say, I was not very happy when I got back the following morning.
*On the bright side, the hotel turned into my favourite place. It was a refurbished castle with about 12 rooms and a michelin-star restaurant inside, owned by a family, and cost about 35 euro a night.