I had a summer job in an office in 1987, after I did my O levels and before starting sixth form. It was with a business that traded exotic woods (less exciting than it sounds).
Although I was the summer temp, the hierarchies mentioned above were alive and well and everybody there was keen to give me advice on how to progress to the dizzy heights of filing clerk. I was starting A levels in physics, maths and chemistry FFS.
My tasks comprised the following:
Each month, putting statements and invoices in enveloped and sealing the envelopes using the roller damper. Somebody else mentioned this upthread.
Going our for fags and sweets for my colleagues.
Ripping the perforated edges off the massive green and white striped sheets of computer paper.
Shredding documents.
Filing (I was crap at it. Like another poster upthread, I just took a punt. It was only later that I realised that Keruang and Sapele are exotic hardwoods and not customers' surnames. In my defence, everyone was bloody handwritten!)
On one memorable occasion, staggering around the office with a massive heavy wooden tray containing cakes, with a strap around my neck, because one of the salesmen had turned 30 and wanted to show some largesse. It wasn't open plan, either: loads of cellular offices and stairwells, so loads of doors to attempt to open with my massive burden!
No email, of course. The office manager spent her days smoking, spraying on Blue Grass and telephoning customers and suppliers in a hilarious posh voice.
My mum had a super 8 camera in the late 60s and filmed her office. Not a computer in sight, of course. They were all smoking, dancing to the radio and buying fags from the tea trolley (the tea lady, in her overall, walked into the shot then reversed out like Acorn Antiques!)