
Marphod |
The chart on d20pfsrd.com (which I assume is from the recent Animal Archive) lists magic item slots for most traditional Animal Companions and Familiars (and some untraditional -- Who on earth takes a DODO as a familiar?).
It is, however, lacking for most of the unusually shaped improved familiars.
Arbiter's have hands and an eye, so a monocle, one or two rings (can its knife be dropped, or is it locked in place?), and maybe a gloves. Probably wrists, possibly a weapon or shield. Can it wear a single lens from a paired set without dizziness? Can you drape a cloak over it effectively?
Augurs MIGHT be able to wear a monocle. Seems like it, though.
Doru's and Severed heads get head, headband, and eye slots. Can you use shoulder slots as well? How about necklaces?
Elementals? No idea.
Nosoi wear a mask; does that mean the headband or eyes slot is taken or not?
Nuglub have 3 eyes. How does that impact lens pairs?
Paracletus are a constellation of lights and crystals. So, uh, rings on long crystals? throw a cloak on top?
Spirit Oni? Uh, I've no idea, either attached or not.
Dragons? I'd probably mix the Quadrupeds (claws) and bipeds, maybe limiting belts to saddles. Although having a headband slot and not a head slot seems weird.
Zoog? It is an amalgam of parts. For all I know, it can wear a ring on each tendril, but no belt/body/neck/head slot.
Harbinger? Got me.

Sitri |

I am pretty curious of this also. I just purchased this book in large part to have documentation for my PFS game about what slots my improved familiar can use. It does not address the issue at all. This strikes me as odd because I know people have been speaking pretty authoritatively about things like the faery dragon and imp having very specific slots and wand capabilities. I thought they were pulling the info from this book.
I guess I should have checked the FAQ
http://paizo.com/pathfinderSociety/faq

spalding |

There was a lot of basic, "duh" information out before this book was published. It was generally assumed that creatures like the fairy dragon and imp having hands, heads, torso, feet and the like could use items designed for those body parts.
Since I don't own the animal archive I can't say as to what it says, but please remember that familiar's and animal companions have been around much longer than this book and these concepts aren't new, so if you read something in a thread it's probably older than the book in question and based on assumptions made at the time.
I'll answer what I'm aware of from pass assumptions:
1. elementals: depends on form -- since these vary widely in appearance I would base it on said appearance, if it's humanoid go with what humanoids can wear, if it's bird shaped then avian based items, et al.
2. Dragons: I've seen dragons wear everything from belts, to helmets to armor, gloves, weapons, boots and necklaces, crowns etc.