Exp. Share/Lucky Egg: both give Exp. Points to a Pokemon holding it even if they did not battle
Any Type-Enhancing Item (for example, Mystic Water)/Corresponding plate (Splash Plate in the case of the Mystic Water): Both boost moves of the corresponding type by 20%.
Lucky Punch/Stick: Boost critical hit ratio by two stages, however, the Lucky Punch only works on Chansey and the Stick only works on Farfetch'd.
Leftovers/Black Sludge: Restore 1/16 of Maximum HP each turn; Black Sludge only works on Poison-types, if held by any other Pokemon 1/16 of Maximum HP is reduced.
Amulet Coin/Luck Incense: Doubles a battle's prize money.
Super Potion/Fresh Water/EnergyPowder: Restore 50 HP.
Full Heal/Lava Cookie/Old Gateau/Heal Powder/Casteliacone: Cure any Status ailment(Poison, Burn, etc.).
Hyper Potion/Energy Root: Restore 200 HP.
Max Revive/Revival Herb: Revive a Pokemon and fully restore HP.
Hope I helped (-o-)