Walkthrough
At the end of Route 17 is Route 16, a very small path that leads you back to Celadon City. There aren't all that many Pokemon Trainers and Wild Pokemon here, but there is another sleeping Pokemon for you to battle. Route 16 is also where you will obtain HM Fly.
Wild Pokemon
Grasses:
Doduo (35%): Levels 18-22
Rattata (30%): Levels 18-22
Spearow (30%): Levels 20-22
Raticate (5%): Levels 23-25
Poke Flute:
Snorlax: Level 30
Pokemon Trainers
Young Couple Lea & Jed: Level 29 Ninetales, Level 29 Rapidash
Biker Leo: Level 29 Grimer, Level 29 Koffing
Cue Ball Luke: Level 29 Mankey, Level 29 Machop
Cue Ball Koji: Level 28 Machop, Level 28 Mankey, Level 28 Machop
Biker Hideo: Level 33 Weezing
Biker Ruben: Level 28 Weezing, Level 28 Koffing, Level 28 Weezing
Cue Ball Camron: Level 29 Mankey, Level 29 Machop
Pokemon Trainers - VS Seeker Rematch
Biker Ruben: Level 48 Weezing, Level 48 Weezing, Level 48 Weezing
Cue Ball Camron: Level 49 Primeape, Level 49 Machoke
Items
Leftovers: ItemFinder
Amulet Coin: From Professor Oak's Aide
HM02: From Girl In House