stub * out +
He stubbed his cigarette out in a saucer because he couldn't find an ashtray.
stuff * up +
I stuffed the exam up.
stumble across/on/upon +
You'll never guess what I stumbled across when I was packing my stuff.
I stumbled across him in the library.
I stumbled upon these photos when I was clearing my room up.
(常指不情願地) 付 (錢)，給 (錢)
He didn't want to pay me back, but I got him to stump up in the end.