comp, pop, set the bait, matches

[kjc0123]

What is the meaning of "comp", "pop", "set the bait", "matches" in the following sentences?

"I went to a casino last night," he announced with his mouth full.  "Which one?" asked Harry Rex.  "Santa Fe something or other, the first one I came to. You been there?"  "I've been to all of them," he said, as if he'd never go back. With the exception of
illegal narcotics, Harry Rex had explored every vice.  "Me too," said Forrest, a man with no exceptions.  "How'd you do?" Forrest asked.  "I won a couple of thousand at blackjack. They comped me a room."  "I paid for that damned room," Harry Rex said. "Probably the whole floor."  "I love their free drinks," said Forrest. "Twenty bucks a pop."  Ray swallowed hard and decided to set the bait. "I found some matches from the
Santa Fe on the old man's desk. Was he sneaking over there?"  "Sure," said Harry Rex. "He and I used to go once a month. He loved the dice."  "The old man?" Forrest asked. "Gambling?"  "Yep." "So there's the rest of my inheritance. What he didn't give away, he gambled away." "No, he was actually a pretty good player."

[Didwot]

Sounds like a detective novel set in the US. Not Raymoind Chandler, unless he was having a bad day, and not Dashiel Hammet.
Anyway
comped = let me in/use for free = (complimentary)
a pop = each
set the bait = prpare to spring a trap on the other person
matches = those books of matches that hotels, bars casinos etc give away with their names on as publicity.