I think I have a good example which I will put behind an SBLOCK because it has not come into play in my current campaign, but it is an example of something I am planning on. . .
[SBLOCK]
On of their early adventures the PCs became friends/allies with a tribe of barbarians whose men of age (and their wives) were all off fighting. Because of their aid and friendship with these barbarians, the PCs were given very simple wooden pendants with a jackal's head (the symbol of the tribe).
Some PCs threw it in their pack and forgot about it - at least one wears it and another sought to sell it off when they got back to civilization.
In the adventure coming up they have a very good chance of running into those barbarians from the same tribe who are on the warpath and who were not in their home territory when the party met the rest of the tribe.
Now, if one or more of the party are wearing the sign of their tribe (in the simple wooden style the barbarian warriors recognize) then any negotiations with these barbarians will be a lot more favorable.
But even if none of the PCs are wearing it, if they notice similar pendants on the barbarians, one might think to pull out their own and show it in an effort to make peace.
However, even if this doesn't happen, the PCs can still try to negotiate, or they can even try to fight and kill the barbarians, or flee, or something else I hadn't thought of. . .
But in this case, if one or more of them keep this particular item, showing how they value their relationships with NPCs (despite the near worthlessness in terms of coin of the item itself) they will benefit from it.
So in this case, it is not about a particular ability or magical item, but a particular quality (keeping, collecting, valuing) that will be of help.
[/SBLOCK]