So I had this Idea...

[Vincent The Dark]

I was thinking of getting a feat on a flying familiar, like a hawk, that gives an item slot. Then, putting Muleback Cords or some equivalent in that slot. Then, using that familiar or companion to carry me from time to time, hold my bags and what not.
Sounds legal (PFS) or not really?

[Avianfoo]

Sounds good to me, provided the hawk can carry that much even with the muleback cords.

Some GMs might not allow the weight to be over the hawks light encumbrance but there is no explicit rule against this in PF. You could always fall back to the "It's maaagic" defense. :)

[Nefreet]

You don't get to change the feat that a familiar starts with. The only way (that I know of) to give a familiar extra feats is to take levels in that one witch archetype that I can't recall the name of right now.

[Weirdo]

As for the encumbrance issue:

Carrying Capacity wrote:

A medium or heavy load counts as medium or heavy armor for the purpose of abilities or skills that are restricted by armor.

Barding wrote:

Flying mounts can't fly in medium or heavy barding.

This can be taken to mean that flying creatures can't fly with a medium load, because it counts as medium armor, which is pretty much the same thing as medium barding just shaped differently.

However there's also the argument that this restriction only applies to mounts and barding and can't be extended back to non-mounts.

I am not sure whether this causes variation in PFS play or just home games. More here.

[Xaratherus]

I can find RAW where animal companions can choose alternate feats, but I do not see rules governing feat choices for familiars (or that they receive feats at all) on the PRD. There's a reference to feat choices for familiars on the PFSRD but not a citation as to where that text can be found in official rules.

[Nefreet]

Familiars get a single feat as listed in their entry in the Bestiary. Usually it's Weapon Finesse.

[Vincent The Dark]

But basically if I can get that feat on a flying high str. familiar or animal companion and add the +8 to str (to carry capacity) from the magic item, the flying carrier sounds legal, right?

[Darigaaz the Igniter]

Animals get item slots too. No need for a custom feat.

[Xaratherus]

I would say yes. However, you'd need a heck of a carrying capacity, since the thread that Weirdo linked lends a pretty good argument that you cannot fly with more than a light load.

Assuming that your character and all his gear weighed, say, 200 pounds, your familiar would need a strength of 23-24 in order for you to fall into its "light load" category.

Now if you're a smaller creature, like a halfling or gnome, this might be a more viable option.

[Sesharan]

Actually, I already do this with my imp familiar, a Heavyload Belt, and the Muleback Cords in PFS. It's a lot of fun. Just remember that Tiny creatures have 1/2 the carrying capacity of an equally strong Medium creature.