Route 11 is a short, grassy route to the east of Vermilion City near Diglett’s Cave. You won’t be able to go to Route 12 further east the first time you visit, but later on in the game the path will open up making central Kanto more accessible. I will try to list everything from the west to the east side of the route.
A Coach Trainer will be waiting near the west side of the route. Speak with him to begin a tough battle with a seemingly weak Pokemon. Use a Fighting-type Pokemon or you might run into some trouble.
Defeat Tomoe to receive P320 and 3 Poke Balls. Just above Tomoe is a lone rock. If you investigate this rock you can find a hidden Revive.
Before going in the route house, search between the building and the trees to the south to find 5 Great Balls.
This should clear all of Route 11. Enter the route house and go upstairs to find Professor Oak’s Assistant. If you’ve captured 30 different species of Pokemon, he’ll add the Judge function to your Pokemon box. Press the Y Button while looking at a Pokemon’s summary to see their individual values.
You won’t be able to go very far into route 12 to the east because a sleeping Snorlax is blocking the way. Your next stop should be Diglett’s Cave.