Well strictly speaking, although logic denotes that you would want to use the cheapest gifts that produces the
symbol, bear in mind which NPC also contributes to the Head of the Household sunstone. It may be in your best interest to use gifts that yield more FP to get you to that goal sooner, without breaking the bank.
Going by the original list, you can indicate that
these are what you can gift if it is a (slightly) cheaper alternative and gives +500 FP:
Denny - Fish (S)
Shea - Fish (S) or Herbs
Will - any flower
Julia - Eggs
Lanna - Fish (S)
Natalie - Blueberry when it is in season
Taro - Pet Food
Gannon - Lumber or Material Stone
Eliza - Chocolate or flowers
Nathan - Urchin when it is in season
Martin - Fish (S)
Ray - Fish (S)
Slater - Emerald
Isaac - Emerald