What does "refresh" mean?

What kind of joke is this?

He is joking here that the person would not be perfect for him if they were actually "perfect", but if they were "co-dependent" and "self-destructive" then they would be the perfect person for him. He says this as a joke because he thinks that he is "co-dependent" and "self-destructive", so if someone else were like that too, then they would be a perfect match.

What's the main difference between "bag" and "sack"? Can't I say "sack" in this context?

In this context, you could use "sack" instead of "bag". A "sack" is a type of "bag". You use "sacks" to store food in large quantities, like the corn in this case. It is a large bag made out of strong material, like canvas. Ex: There was a sack of flour in the cupboard that I couldn't reach. Ex: Can you get me a small bag of crisps for the road? Ex: Sarah thought she could turn the old sack she found into a doormat.

What's "checkout" and "register"? How are these different?

The two are often used interchangeably but have slightly different meanings. A "checkout" can refer to the area or point where goods are purchased, such as a checkout line or checkout counter. Meanwhile, a "(cash) register" refers to the computing machine itself which processes transactions. In some cases, "checkout" is also used as a verb to indicate the action of purchasing something. Ex: Please proceed to the checkout point. Ex: You can pay for your products at the cash register.

Does the phrase "get in trouble" a passive voice? Would there be an active voice version of it?

That's an interesting question. The phrase "to get in trouble" is actually in the active voice already, despite using the verb "get". The reason this is active is that nothing/no one is acting on the speaker. There is no natural-sounding way to put this expression in the passive voice, but there are passive voice alternatives to the expression in this context. Ex: I got yelled at by the teacher for talking in class. Ex: I was scolded for talking in class. ("to scold" = express strong criticism of someone because of their actions or behavior)

Could you explain more about the expression "win at something"?

To "win at" is a phrasal verb that means to come first in doing something like a competition or a game. Here he says he never "wins at canasta", which means he never is successful in achieving first place in the game canasta. This phrase is normally used when referring to winning a game, however, it can also be used to express earning a reward from winning something. When something is earned, a noun often comes between "win" and "at". Here's a couple of examples: Ex: I won that toy at the carnival. Ex: I can beat her in most games, but she wins at chess every time.