Instructions
Insert the Game Boy Advance GameShark device into the Game Boy Advance game slot. Select the "On" setting on the GameShark. Insert "Emerald" into the slot on the GameShark. Turn on the Game Boy Advance system.
Press right on the "D" pad to access preloaded codes for "Emerald." Navigate through the list until you see "Access Mod Shop," "All Key Items" and "All Misc. Items." Navigate to each of those three cheats and press the "A" button. The cheat will flash when activated. Return to the GameShark's main menu.
Press the "Start" button after activating cheats to access the main menu of "Emerald." Load a saved game. Visit any PokeMart and press "L," "A" and "Select" simultaneously. Speak to the PokeMart clerk to access the Mod Shop. Select an item and press "A" to confirm its purchase.