For me it was people bringing boxes full of 5.25" floppies and multiple external floppy drives...
The fun thing, though was the postal swapping, which developed into an art-form involving defrauding the postal service (wax over the stamps etc. to let you scrape off the post mark and reuse the stamp), and dropping the envelope entirely (affixing address labels and stamps straight onto the floppies and just tape a floppy cover in place - some didn't even use a proper cover, but just taped a small cover over the hole in the floppy to prevent dust).
All in the interest in reducing turnaround times and cost, given that top swappers would turn around a ridiculous number of floppies on a daily basis just to keep their network intact - slow down, and be unable to provide stuff that was new enough, and people would drop you in favour of contacts who provided newer stuff (which by the late 80's increasingly meant the best connected people expected "zero day" releases, and then went off into insanity where people expected cracks of games before they were released - some games were released in cracked form before they were even finished, with levels missing etc.)
This was more widespread in Europe than the US, where strict national telecoms regulation in most countries until the EU started deregulating it, coupled with per-minute billing for local calls, meant modem usage remained low until well into the 90's.
