From StrategyWiki, the free strategy guide and walkthrough wiki

You've come passing through here before on your way to meet your rival. There still isn't much to do here. Now that you have received your first set of Poké Balls, you can buy them from the Poké Mart in town. Buy 10 Poké Balls and you'll receive a Premier Ball for free! The Premier Ball has the same catch rate as a regular Poké Ball, but it looks nicer.

If you speak to man in the first house on the right as you enter Oldale, he will give you a free Potion. Also, don't forget to replenish your Pokémon's hit points at the Poké Center, especially if you damaged a Pokémon that you then caught. You can head north back to Route 103 where you fought your Rival and attempt to catch a Wingull. Otherwise, that direction is a dead end. When you're ready, you can now head into Route 102 which was originally blocked by a man studying a rare Pokémon's footprints.

Oldale Poké Mart
Potion	300
Antidote	100
Paralyz Heal	200
Awakening	250
Poké Ball	200

#278 Wingull

This seagull of sorts is not very rare over ocean; once you hit the high seas, you'll be running into swarms of them, and their evolved form Pelipper, so don't fret if you can't get one now. If you want one now however, it might take a while, since they're a bit rare on land. Overall, their stats aren't too exiting, but he possesses Water Gun a basic water move, making him useful for players who didn't choose Mudkip as their starter, especially for Torchic users, who would lack an advantage at the first gym. Overall, with Wing Attack available after a few levels of training, he makes a useful member to your team for the early part of the game.