Rare items

[Beekeeper]

Items such as firefly flower, truffle, stone tablet, treasure, bottles, etc. besides giving them as gifts, what is the point of getting these things?

[Ru-Ne Ni-Chaan]

Of course these item need to "Complete Item List"
so beside you give them to some people you just ship them at least one of them
to complete your ship item list.

[Veggie Angel]

Items such as firefly flower, truffle, stone tablet, treasure, bottles, etc. besides giving them as gifts, what is the point of getting these things?

These are items needed if you intend to complete your fishing list but the stone tablet and bottle are multipliers. If you put any bottles you collect and any stone tablets you collect in your rucksack before you go to bed, when you wake up each morning you will receive 1 mining degree point times the number of game years you have played for each stone tablet, and 1 fishing degree point times the number of game yearts you have played for each bottle.

The firefly flower is Will's favorite gift and the legendary treasure is Lily's favorite gift. These gifts make great birthday gifts for either character.

The truffle after you ship one can be a substitute in a recipe using mushrooms for additional stamina. It can be used in the Cooking Festival if you want an edge for a winning entry. The bottle can be used to get the recipe for Fish Natto (from Nick) and is an ingredient in that recipe. The recipe will fail if you don't have a cooking degree of at least 45,000 points.

Because of their rarity, they are also more valuable than their more common counterparts

[NightSurfer]

They ship for more and fill your shipping list in the short way.