How do I get to saffron city?

To get past the guard, walk past him while holding one of Soda pop, Fresh Water or Lemonade. These can be obtained on the roof of Celadon Department store for less than 300 dollars.

In order to get past the sleeping pokemon, you must play the PokeFlute next to it. The PokeFlute is obtained from Mr. Fuji after rescuing him from the top floor of the Lavender Town Pokemon Tower. In order to do this, you require the Silph Scope so you can see ghosts. The Silph Scope can be obtained after defeating Giovanni in the Rocket base, accessed by pressing the switch behind the poster in the Celadon Game Corner.

The Coin Case can be found in the restaurant in Celadon City.