When we first started dating, I used to always plug the toilet like clockwork when I'd have to go at the gf's place. I swear her toilet had the weakest flush. It wasn't a big place, so there was always a panicked attempt at "stealth-plunging".
Dunno if I was just holding it too long, or just nervously wiping too much.
Also in a pinch (

), apparently hot, hot water is a lifesaver if you don't have a plunger. Just start slowly pouring it into the bowl. Of course, if this is one of those tricky "stealth-plunging" situations, finding a way to get that much hot water from the sink to the toilet noiselessly and without asking for a pitcher is another can of worms.