Route 104 - North
Continue along into the Petalburg Woods. As you do, though, take note as you cross the bridge; once you get to the south side, Cut down the tree to your right to get a Revive .
Cut down the tree just to the southeast as you enter the woods. First go north of the small grassy area nearby and examine the empty tile to find a Tiny Mushroom .
As you go along the path, you’ll see a yellow-shirted kid standing around; the camera viewpoint may put him behind a tree and make him hard to see. Speaking with him will net you the Miracle Seed , an item that will boost the power of the holder’s Grass moves by 20% which is quite a bit!
Further to the east is a large mossy rock; you may not know, but this rock is what you can use to evolve Eevee into Leafeon if you level it up near here.
Near the mossy rock, just to the south, is a Great Ball . After grabbing the ball, jump over the ledge to the south, then continue south and over another ledge. Go west and pick up the X Attack .
Now, to the southeast, you’ll see how the taller, darker grass makes two "L" corners, right? Examine the tile squished between the sides of the northwestern "L" corner to find another Tiny Mushroom . Now continue further along the path southward to Route 104.
Route 104 - South
Here, go south and west to Mr. Briney’s shack near the shoreline. Speak with him inside and you’ll find him chasing Peeko around the table. Okay… Anyhow, block them and speak with Mr. Briney to opt to take a ride to Dewford.