Key Items

Black Materia: used to cast Ultimate Destructive Magic (Meteor)
Temple of the Ancients

Blonde Wig: for Cloud's cross-dressing
Wall Market

Cologne: to spice up Cloud's aroma
Wall Market

Cotton Dress: for Cloud's cross-dressing
Wall Market

Deodorant: exchange for Pharmacy Coupon
Wall Market

Diamond Tiara: an accessory for Cloud's cross-dressing
Wall Market

Digestive: exchange for Pharmacy Coupon
Wall Market

Disinfectant: exchange for Pharmcay Coupon
Wall Market

Dyed Wig: for Cloud's cross-dressing
Wall Market

Flower Cologne: to spice up Cloud's aroma
Wall Market

Glacier Map: map of the Great Glacier
Icicle Inn

Grass Tiara: an accessory for Cloud' cross-dressing
Wall Market

Huge Materia: exchange mastered materia for Master Materia; four in all
North Corel, Fort Condor, Underwater Reactor, Shinra No. 26 (Rocket)

Key to the Ancients: helps find reveal White Materia
Below North Continent (accessible via Submarine)

Keycard 60: accesses floor 60
Shinra Tower

Keycard 62: accesses floor 62
Shinra Tower

Keycard 65: accesses floor 65
Shinra Tower

Keycard 66: accesses floor 66
Shinra Tower

Keycard 68: accesses floor 68
Shinra Tower

Keystone: use to enter Temple of the Ancients
Dio's Showroom

Leviathan Scales: extinguishes flames in Da-Chao Statues
Underwater Reactor

Member's Card: allows entrance to the Honey Bee Inn
Wall Market

Midgar Parts: use them to complete model of Midgar
Shinra Tower

Mythril: trade for item in Weapon Seller's House
Old Man's cave (middle of East Continent)

Pharmacy Coupon: trade for item in Pharmacy
Wall Market

PHS: allows you to switch between parties at save points
Kalm

Ruby Tiara: an accessory for Cloud's cross-dressing
Wall Market

Satin Dress: for Cloud' cross-dressing
Wall Market

Sexy Cologne: to spice up Cloud's aroma
Wall Market

Silk Dress: for Cloud's cross-dressing
Wall Market

Snowboard: use to get from Icicle Inn to the Great Glacier