Celadon City

From the Pokémon Center, head east to find a Nugget, then continue west to find a Rare Candy. Enter the building to the left of the path's branch to reach the Celadon City Condominiums.

Ascend the condominiums to the roof and enter the penthouse to find TM44 Play Rough.

Backtrack to the Pokémon Center entrance and head west. You will encounter Brock, who will give you Pewter Crunchies and a cup of Tea. The Tea is crucial for progressing to Saffron City.

Enter the Condominiums and explore the floors. On the third floor are the GAME FREAK offices (currently offering nothing). On the roof, near the extractor fan, collect 3 Health Candies.

West of the Condominiums is the Celadon City Department Store. Use the lift or stairs to access different floors.

The second floor features a TM shop and a Poké Mart. The TM shop sells TMs such as Dragon Tail, U-turn, Iron Tail, Waterfall, Tri Attack, Bulk Up, Shadow Ball, and Hyper Beam. The third floor has a gaming shop where you can receive TM03 Helping Hand.

On the fourth floor, you can purchase evolution stones: Fire, Thunder, Water, Leaf, and Ice.

The fifth floor sells accessories for your partner Pokémon. On the roof, purchase a Fresh Water, Soda Pop, and Lemonade from the vending machine. Speak to the girl nearby and give her one of each drink to receive TM06 Light Screen (for Fresh Water), TM09 Reflect (for Soda Pop), and TM07 Protect (for Lemonade).

East of the fountain, enter the Game Corner. Explore the area to find several hidden items. Eavesdrop on Jessie and James, then search near them and around the counter for more hidden items. Approach the Rocket Grunt and search the potted plant and space between room separators for additional hidden items.