There's one of those memes going around where people list all kinds of things they consider essential to any comic collection of any worth. I read a couple of them, found that I only had about a quarter of the things listed, and realised I didn't care.
So here's my short version of things to claim you have in your collection if you want to look cool (but you don't actually have to own them).
1. A current obscure title that nobody else has heard of, which goes to show how cool you are for being aware of it.
2. A title that everyone has heard of but doesn't think is that special, but for which you have a cunning argument for why it is cool.
3. A title that everyone already knows is cool, just to show that you have some common ground with the rest of comic fandom.
4. A golden age title that nobody else has heard of (you can make one up if you like as there are lots of short lived golden age comics that sank without trace).
5. An indie comic that nobody else has heard of because only 5 copies were ever printed.
6. Some outrageous kitchy light-hearted silver age element that could only be reused today with heavy-handed symbolism or knowing self-reference.
7. A comic, or particular run of a comic that has been out of print for at least twenty years, which you can lobby for collected reprints of.
8. A title you think must be very cool because you completely fail to make any sense of it. If it's a manga, you can't even work out whether to read it left to right or right to left because it makes as little sense either way.
9. A hideously expensive deluxe collection of some title . I mean if people are going to pay hundreds of dollars for it then it must be good, right?
10. A comic so obscure that it was never actually published. Or even written.
Edit: Damnit, I just thought of another one. Okay, consider this a substitute for any of the other ones, or an additional feature of one of them.
Ω. A comic with which you have some kind of personal connection, even if it's only that you once stepped on the inker's toe at a con. Anything works providing you can spin it into an anecdote to bore friends, acquaintances, and complete strangers for the rest of time.