I often ask the receptionists if they want anything from the coffee shop or canteen as you never know when you need a favor with a late parcel delivery or taxi etc.
I offer the security guards too but they are not allowed to drink or eat on duty.
I also make a point of thanking those I don't know I came in on a Monday expecting to have to finish tiding up refreshments from a late Friday meeting only to be pleasently suprised the cleaners had colated stuff from around the large open plan office and neatly stacked it all to be taken away. Next time I spotted a cleaner I asked him to pass my thanks on.
On a lighter note I had to empty a paddling pool of rubber ducks after a hook a duck competition. (another story!) we decided to pour it down the sinks in the ladies as it was cold outside, and promptly flooded the ladies toilets as the sinks could not cope with the water. We managed to get an emergency cleaner who was really helpfull and good hummored about it all. I later trac ked her down with the spare rubber ducks which she wanted for her grandson and made her day!