You can revisit Rocket Town anytime after you obtain the Highwind on Disc 2. Head into the Weapon Store on the left side of the screen and you will find a treasure chest containing a Fourth Bracelet, which is a very powerful piece of armor.

There is also a treasure chest in the back of the Item Store that contains a Guard Source.

After the Shinra Rocket No. 26 Launch

You can also revisit Rocket Town one last time after you have retrieved the fourth and final Huge Materia from the Shinra Rocket No. 26 after it gets launched into outer space during the Rocket Town / Cosmo Canyon sequence (Disc 2). Check out the Rocket Town / Cosmo Canyon Walkthrough page for more information about that section of the game.

Return to Rocket Town and speak to the man in front of the Item Store three times, and he will reward you with the Venus Gospel, Cid’s Ultimate Weapon.