Quote Originally Posted by Jar View Post
stop reading after that..
That's unfortunate, however it seems that aside AF related stuff they are pretty open to what can and can't be shared.

Artifact equipment, mythic weapons
Moogle storage slips
Items related to campaign codes
Quest-related items
Mission reward items, add-on bonus items
Synthesis skill and rank-related items
Items related to the Trial of the Magians

Guess that answers the question about not being able to give friends seals you don't need and want.