This is a great idea for a poll
I'm really interested to read people's responses.
I wish that the T2k games I was involved in lasted long enough to reach the McGuffin stage but sadly they were typically too lethal for characters to survive long enough. The games just weren't enough fun to sustain a campaign so they ended before we could get into those various modules.
Having said that, I wanted to run a T2k campaign where the PCs hear rumours of a crashed Luftwaffe C-160 Transall supposedly laden with German ration packs and ammunition. The aircraft and its cargo did exist but it had crashed in remote woodlands and nobody was entirely sure where it was. I wanted to use it as a way to encourage the PCs to explore the region, the lure of food and ammo I believe would be sufficient to get them to do so.
So in that sense I think it qualifies as a McGuffin - so in that sense, I voted "Other".