Walkthrough
With your Rival defeated, you will be able to proceed north of Cerulean City on Route 24. This path is home to Nugget Bridge, one full of loads of Pokemon Trainers looking to battle. Defeat them to earn access to Route 25 in hopes of eventually meeting Bill at his Sea Cottage.
Wild Pokemon
Grasses:
Oddish(FireRed)/Bellsprout(LeafGreen) (25%): Levels 12-14
Caterpie (20%): Level 7
Weedle (20%): Level 7
Pidgey (15%): Levels 11-13
Abra (15%): Levels 8-12
Kakuna(FireRed)/Metapod(LeafGreen): Level 8
Metapod(FireRed)/Kakuna(LeafGreen): Level 8
Surfing:
Tentacool (100%): Levels 5-40
Magikarp (100%): Level 5
Horsea(FireRed)/Krabby(LeafGreen) (60%): Levels 5-15
Krabby(FireRed)/Horsea(LeafGreen) (20%): Levels 5-15
Magikarp (20%): Levels 5-15
Horsea(FireRed)/Krabby(LeafGreen) (84%): Levels 15-35
Gyarados (15%): Levels 15-25
Psyduck(FireRed)/Slowpoke(LeafGreen) (1%): Levels 25-35
Pokemon Trainers
Bug Catcher Cale: Level 10 Caterpie, Level 10 Weedle, Level 10 Metapod, Level 10 Kakuna
Lass Ali: Level 12 Pidgey, Level 12 Oddish, Level 12 Bellsporut
Youngster Timmy: Level 14 Sandshrew, Level 14 Ekans
Lass Reli: Level 16 Nidoran Male, Level 16 Nidoran Female
Camper Ethan: Level 18 Mankey
Team Rocket Grunt: Level 15 Ekans, Level 15 Zubat
Camper Shane: Level 14 Rattata, Level 14 Ekans
Pokemon Trainers - VS Seeker Rematch
Youngster Timmy: Level 19 Raticate, Level 19 Ekans, Level 19 Zubat
Youngster Timmy: Level 27 Raticate, Level 27 Ekans, Level 27 Golbat
Youngster Timmy: Level 52 Raticate, Level 52 Arbok, Level 52 Golbat
Lass Reli: Level 20 Pidgey, Level 20 Nidoran Female
Lass Reli: Level 28 Pidgeotto, Level 28 Nidorina
Items
TM45: On Ground
Pecha Berry: ItemFinder
Fame Checker: Defeat Rival