Pokémon Ruby and Sapphire/Slateport City

Slateport Beach
As soon as you arrive you will be in Slateport's beach and will encounter more than a couple trainers on your way up to the city. Talk to the little girl with the pink inner tube and she will give you a Soft Sand just for talking to her. The trainers aren't a big deal but will offer some experience points which will be useful in your next encounter with Aqua/Magma.

In Ruby/Sapphire


 * Sailor Huey


 * Tuber Ricky


 * Sailor Edmund


 * Tuber Lola

In Emerald


 * Sailor Huey


 * Sailor Edmund


 * Tuber Hailey


 * Tuber Ricky


 * Tuber Lola


 * Tuber Chadley

At the north west part of the beach is Seashore House. The owner of this house loves watching heated battles, and if you can defeat all the trainers in the house, you get a special price!

In all versions


 * Beauty Johanna


 * Tuber Simon


 * Sailor Dwayne

Talk to the trainers after the battles. For putting up such an interesting fight, he'll give you half a dozen bottle of Soda Pop! It restores 60 health per use, pretty much instantly refilling your Pokemon's health during this part of the game. While you can't take the challenge again, you can buy more Soda Pop from the owner for 300 each.

There's a lot of hidden items on the beach. There's a Heart Scale hidden under the westernmost green umbrella. Search the westernmost beach chair for a Great Ball. There's also a Revive around the western shoreline and an Ether southeast of the girl who gave you the Soft Sand.

Deliver the goods!
With a busy market, a club, a museum and a contest hall(a battle tent for Emerald players), there's a lot to see and do. You still have to deliver the Devon goods, so go to the shipyard to look for Stern.

Where's Captain Stern?
The shipyard is where new ships are built and old ships are sank. Stern isn't around and the man reading the blueprints will confirm this. With nothing else to do, head outside and south to the Oceanic Museum.

The Oceanic Museum
When you first arrived, you might've noticed the long line of Magma/Aqua grunts waiting outside, blocking the entrance. Once you've spoken to the man at the shipyard, the line will clear and you can finally enter. The admission fee is 50, though if you have less than that the receptionist will think you are a grunt and let you enter for free. You'll immediately notice Team Magma/Aqua grunts all over the museum, and the first one you meet is the same grunt you battled before! He'll give you TM46 (Thief) so that you'll leave him alone. Thief is an interesting Dark Type move that let's you steal the opposing Pokemon's held items, but it's a pretty weak move.

Walk upstairs and you will meet Capt. Stern. After finally giving him the Devon goods you'll be confronted by two grunts who'll challenge you to a battle.

In Ruby


 * Team Magma Grunt


 * Team Magma Grunt

In Sapphire/Emerald


 * Team Aqua Grunt


 * Team Aqua Grunt

Once you defeat the grunts their leader will show up. After warning you not to meddle in their business any further, they will leave.

Hyper Contests
You should also go into the contest building (the red building with the grey roof) and talk to the little girl inside and she will give you a Pokéblock case. A sailor near the stage will give you TM41 (Torment) for listening to him.

The Battle Tent
In Emerald you obtain the Pokeblock case from the little girl in the Lilycove contest hall.

Talk to the woman wearing a dress in the building next to the Pokémart and she will give you a Soothe Bell and a scarf if your first party Pokémon is in excellent condition (use the Pokéblocks).

Items

 * Great Ball: Hidden South west of the Seashore House, under the blue towel laying on the beach.
 * Ether: Hidden on the south-east corner, directly south-east of the two children, and east of the beach towel.
 * Revive: Hidden at the southern portion of Route 109 beach. It is one cell north of Mr. Briney's landing point and five squares west.
 * Heart Scale: Hidden south of the Seashore House, under the green parasol.
 * Heart Scale: Hidden one square north of the old man with his Zigzagzoon.