Items

A Trainer can have up to 350 items at the start of the game. Items can perform various actions:
 * Catching Pokémon or assisting with it (Razz Berry).
 * Attracting Pokémon to your location with Lure or Incense.
 * Gain more experience (Lucky Egg).
 * Restore HP with Potions or Revives.
 * Hatch Eggs with Incubators.

The amount of items that can be carried can be increased by 50 by purchasing the Bag Upgrade from the Shop for 200 PokeCoins. This can be done up to a maximum of 1000.

Restorative
Use these items to restore HP to Pokémon, or revive them if they have fainted.
 * Potion
 * Super Potion
 * Hyper Potion
 * Max Potion
 * Revive
 * Max Revive

Enhancing (Trainer)
Use these items to receive a temporary effect on the trainer only.
 * Lucky Egg
 * Incense

Enhancing (PokéStop)
Use these items to apply an effect to a Pokéstop, when can be utilized by other nearby trainers.
 * Lure Module

Catching Pokémon

 * Poké Ball
 * Great Ball
 * Ultra Ball
 * Razz Berry

Egg-Related
These items relate to Eggs and their hatching process.
 * Eggs
 * Incubators

Other

 * Camera