Note, most items have more than one use. The others are creative uses and most are not exactly... pleasant.

Skill Items
Small Net - Used to gain 1 level in hunting
Large Net - Used to gain max hunting 
 Stone Dagger - Used to gain 1 level in fighting 
Metal Dagger - Used to gain max fighting
Small Branch - Used to gain 1 level in gathering
 Large Branch - Used to gain max gathering
 Baby Magic Mouse - Used to gain 1 level in foraging
Adult Magic Mouse - Used to gain max foraging
Small Pouch - Used to gain 1 level in healing
Large Pouch - Used to gain max healing
Star Fragment - Used to gain max skills

Healing Items
River Jelly - Used to heal a pollen sneezing disease
 Lily Roots - Used to heal a fever disease
 Scorpion Venom - Used to heal a blood cough disease
Itchy Leg Hair - Used to heal a rotting tooth disease
 Golden Herb - Used to instantly heal anything

Color Morph Items
 Sun Fruit - Used to awaken a Color Morph
 Color Drop - Used to allow a Color Morph to switch colors at will, although they will always have to revert back to their true color [ Bonus Attack of 5-10 ]
Fairy Dust - Used to give Color Morphs magic relating to their true color [ Bonus Attack of 15-20 ]Rainbow Silk - Used to permanently change true color/pattern or seduce Prism

Chimera Morph Items
Tarantula Meat - Used to awaken a Chimera Morph
Scorpion Tail - Used to awaken a Chimera Morph
Odd Meat - Used to awaken a Chimera Morph
 Dragon Scale - Used to awaken a Chimera Morph or instantly seduce a god.
Fresh Venom - Used to possibly increase a Chimera Morph's venom level
Magic Heart - Used to permanently change type of Chimera morph or seduce Chimera

Winged Morph Items
 Frog guts - Used to awaken a Winged Morph
Baby Feathers - Used to gain 1 level in flying
Bird Feathers - Used to gain max flying
Halo's Feathers - Increases flying to 6 or seduce Halo

Plant Morph Items
Cedar Tree Seeds - Used to awaken a Plant Morph
Flowers - Used to gain 1 defense point and three extra moons of life. 20 can be used to make a flower crown.
Rose of Life - Used to double your lifespan.
Lily of The Valley - Used to become impervious to disease or seduce Poppy

Banshee Morph Items
Owl Lungs - Used to awaken a Banshee Morph
Air Bubbles - Used to increase lung capacity by 5%
Lizard Lungs - Used to decrease chance of sickness by 5%
Bottled Screams - Used to give screeches an actual attack stat and prevents deafness or seduce Screech

Crystal Morph Items
 Shiny Rock - Used to awaken a Crystal Morph
 Shiny Necklace - Used to increase density of Crystal Morph
Iron Stone - Used to sharpen crystals on body to increase attack by 5-10
Black Diamond - Used to max out density of Crystal Morph and give 10-20 bonus attack or seduce Corundum

Cloud Morph
 Cloud Puff - Used to awake a Cloud Morph
Floaty Rain - Used to prevent Cloud Morph's from getting sick
Snow Sheet - Used to allow Cloud Morphs to choose their weather pattern
Contained Lightning - Used to allow Cloud Morphs to summon lighting once every other moon or seduce Gale

Mermaid Morph
Dried Seaweed - Used to awaken a Mermaid Morph
Sentient Bubble - Used to give a water bubble an instant revival
Jellied Water - Used to make bubbles grounded and not float away
Selkie Venom - Used to give Mermaid Morphs a venom level or seduce Siren

Corruption Morph
Vial of Acid - Used to awaken a Corruption Morph
Slug Mucus - Used to increase the acidity of their acid
Silver Necklace - Used to purge a Corruption Morph and leaks acid comparable to their sins
??? - Not a tangible item. Seems to increase corruption. Will entice Hollow.

Ghost Morph
Clean Bones - Used to awaken a Ghost Morph
Shattered Diamond - Used to decrease chances of interacting
 Amulet of Silver - Used to make self impervious to disease
Herbal Water - Used to make a Ghost Morph a poltergeist or seduce Wisp

Extra Items
Steel Claws - Used to increase attack by 5-10
 Odd Rock - Used to give a random hidden morph
 Glitter Rock - Used to give a certain hidden morph
 Glitter Cage - Used to get a second character, cannot use if you have 2 already
 Bright Card - Used to summon an event for everyone to get items
 Pineapple - Used to get an 100% kill, at the sacrifice of a 50% hint chance
 ??? - Used to ask a favor from a god, not a tangible item, instant favor and increases chance of demigods from kits with that god.

***If you want to know if you have a hidden morph... just ask.***