I think these are good things to have, for every Modern Hero or Heroine. Too few people have Arch Enemies, to keep them on their toes. And everyone needs a Concubine/Fuckbuddy/Bottom Quark. Except those whose spouses would object, I guess.
But Reene's post got me thinking: what other characters do we need in our lives? I suggest the following:
Self-explanatory. Everyone needs a Best Friend to share confidences, to bounce ideas off, to stand up to bullies, to provide comfort and good advice when you're down.
The guy who is always your opposite in intramural basketball games, the giant robot pilot in another platoon who always vying with you for the most kills, the girl in your class who is almost as pretty as you, and a better duelist, etc. You'll have a beer with your Friendly Rival when the contest is over, which you would never do with your Arch Enemy, but you certainly wouldn't share confidences with them. That's what the Best Friend is for. Alas, Friendly Rivals tend to get killed a lot, while protecting you, and need to be replaced on a regular basis.
Think Obi Wan Kenobi, or Gandalf. Older, usually male, with at least some white or gray hair. Everyone's gotta have one.
Helpful in getting into foolhardy predicaments that you have to get them out of, and advancing the plot of your life. Also: helping them solve their little problems is good experience for when you'll be an Avuncular Mentor yourself, some day.
Cat, dog, large lizard, monkey, horse, supernatural or alien beast. Something you can have a relationship with. Fish and ant farms don't count.
If you are female, substitute Bishounen Sidekick. Basically, a Fuckbuddy without the fucking, or a Best Friend of the opposite sex, but without the sexual element, so they can be a friend without a lot of erotic role-confusion.
Current Crush (suggested by Taylor)
Person who is the current object of your erotic fantasies, which will probably never be fulfilled, and who may well be replaced with another Current Crush in a month or two.
So these are the associates that a Modern Hero or Heroine needs. But what about a Postmodern Hero or Heroine?
Or maybe that should be Postmodern Antihero or Antiheroine. But whatever. I can come up with only three definite ones:
See above. Concubines are always needed.
More of an organization than a particular person, this can be Media, Government, The Patriarchy, Giant Shape-Changing Lizards, or whatever you please.
Very few Science majors among the Postmoderns. Lots of Humanities majors, lots of publishing activity. Ya gotta have an editor.
And that's all I can think of. I'll take submissions of further Postmodern Hero/Antihero associates if you can do better.