stub out; stuff up; stumble across/on/upon; stump up

stub * out +
捻熄 (香菸)
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.

stump 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.