Here's some guidelines from Niamh:
Hey guys! This are my guidelines for foraging additions. Hope it helps!
a) What Goes Where: The key word in "flavor foraging" is "flavor." Objects should be feasible for the location they are added to - something an NPC would regularly drop or lose track of there, something produced there where an excess might be lost (a granary might have a few fronds of of wheat, for example), or something that could be found organically (a seed, a certain kind of animal part) in the location.
b) Lore: At the higher levels of Forage (master and up), it should be possible to find rarer, stranger items. City Lore should be added to the room to explain it; don't tell the player what's there, tell them the story of why something along those lines could be.
c) Crafting: Generally speaking, inexpensive crafting ingredients should be used for forageables rather than any sort of finished product - there may be rare exceptions where appropriate, as long as the rest of the guidelines are applied.
d) Wilderness Scarcity: As sectors already have standard forageables, be scarce with adding flavor forageables to wilderness rooms. Check to make sure it isn't already covered before making additions.
e) Realism: Bear in mind that each forageable item can be foraged 3 times until the room is too picked over. There are some things that just don't make sense to add anywhere; books, for example, should always be avoided. No one could find 3 copies of the same discarded book (books are rare and expensive as it is) in the same place multiple times. That logic should kept in mind for all forageable items. Could it be found there three times by a truly dedicated forager?
Skill < 36: Objects should be 5 silver or less from NPC vendors.
Skill < 50: Objects should be 20 silver or less from NPC vendors.
Skill < 60: 50 silver or less from NPC vendors, add City Lore.
Grandmaster: Objects can be strange or rare, and should have City Lore.
Too tempting with silver scarcity considered.