You won’t be in too many battles before the next city, so spend your money on a couple of Potions and a ton of Poke Balls. The next building west of the Poke Mart is the Trainer School, though there’s nothing important there at this time.
On the northwest corner of town is a lone bush that can be chopped down later on in the game. If you interact with the left side of the bush, you will find a secret potion! Many secret items that have set locations such as this will reset every day. Come back tomorrow to find another Potion! When you’re ready to continue your adventure, head west to Route 22.