Delivery people... I've had my laptop stolen by a fake delivery worker who cleaned up the building.
An UPS or DHL uniform will get you most everywhere, and you have an excuse for carrying bulky stuff.
Edit: Kevin Mitnick's The Art of Deception is an oldie but goodie detailing most of this stuff.
https://www.goodreads.com/book/show/18160.The_Art_of_Decepti...