Read on, I've got three!
In the early 1960s, in the days of steam, I used to travel occasionally on the Oxted line up to London in the a.m. peak. The train we caught would stop at Selsdon for signals and I would notice doors opening and slamming, despite the platforms on the "main" line having been closed for several years. Must have been a daily occurrence.
Years later in the days of DMMUs on the Reading to Tonbridge line, the last one from Reading to Guildford used to continue non-stop to Redhill (unadvertised of course) as parcels only. Those in the know would usually be allowed a ride if the guard was asked nicely. I would even get let through the barrier at Guildford ("Last train's gone" "yeah, there's the Parcels" "ok then, good luck"). One night the driver even stopped at Reigate for my mate to get out.
Over to Sardinia about 20 years ago and a walk in the mountains got delayed and diverted due to encountering aggressive sheepdogs. That left us in a hurry for the last narrow-gauge train back to the town we were staying in, but luckily we made it - just - and flagged down the train at the tiny halt as it came round the corner. The single-unit railcar stopped but oddly the driver seemed reluctant to open the doors, and it turned out we weren't at a stopping place at all, just a PW house - the halt was a mile or so was further on! After explanations all round in two languages the guard laughed it all off as stupid foreign tourists getting lost, and refused my offer of cash. For once we were lucky my map-reading skills were so crap!
Shame such helpful but unofficial practices by kindly railwaymen couldn't happen today.