I originally posted this to the bug report system, but it's really not a bug, so I figured I'd ask here.
According to the Pathfinder Society FAQ, the "Extra Item Slot" feat meant for animal companions and familiars works differently than normal Pathfinder:
http://paizo.com/paizo/faq/v5748nruor1fq#v5748eaic9p51
In short, rather than animals automatically getting all slots listed for their type in the Animal Archive chart, they only get barding and neck slots, and only if their body can physically use neck items or barding. (A snake as noted has neither slot).
In PFS, the Extra Item Slot feat, rather than allowing the animal to use slots they don't have listed in the chart, instead allows them to 'unlock' one of the slots they DO have listed on the chart, if they don't have it already.
Is there any way to implement this? Or has anyone come up with a custom file for it?
-j