The captain on the ship references a whirlpool. In the manga Luffy's boat was caught in a whirlpool and Luffy hid in the barrel.
In the manga Luffy's barrel was found by Coby washed up on the shore where Alvida's crew were unloading their spoils.
The entire scene, in the manga, with ALvida's crew, took place on land. His Devil Fruit powers were never shown until he struck Alvida in the face and not the gut, the way the anime depicts.
In this first episode Nami actually appears before Luffy does. Story wise, Nami isn't actually scene until after Zoro joins Luffy. The way she seems ready to raid the pirate ship seems to imply she knew the ship would be attacked.
As Luffy escapes with Coby his eyes meet Nami's and there is a long look. This is most likely a nod to the creation of One Piece. Eiichiro Oda wrote two one shots where a Nami-like character was with Luffy.
In this episode, the English version credits Zoro's voice actor. Though, he had no spoken lines. The Japanese version did not list any credits.