I think it would be to keep things in there.
James L. Pocket
Most suits come with pockets sealed to prevent them from catching or bunching during transport and sale.
Some dress shirts commonly have holes, which are pockets. The pockets are just a apart of the shirt for stylish accent.
Many women don't wear shirts with pocket but they are usually on the left
Pockets are more prominently on the left side of a shirt because most people are right handed. This allows a right handed person to access the pocket easier.
I am not sure about other parts of the country, but at the store I work at in Idaho it is dark blue shirt, no pockets; and black slacks.
The extra pockets are useful when wading out in the streams. But if you are only shore fishing then a tackle box will work fine. Otherwise you could just use a cheap / old shirt with extra pockets.
Pen/Pencil Money Handkerchief Glasses Cigarettes
Depends what you call "traditional". The guayabera shirt is claimed to be originated in Cuba or Mexico. I can tell you the Traditional Cuban guayabera shirt is traditionally designed with 4 pockets on the front, alforzas or pin tucks running on top of the pockets from top to bottom. The Cuban shirt has three rows of alforzas on the back with a triangular shape on top of each row; I've heard this symbolizes the Cuban flag. The Traditional Cuban guayabera does not include any embroidery and has decorative buttons on each of the pockets. The bottom of the shirt also includes a design similar to the top triangular shape where the alforzas originate. I hope this description helps since it is hard to describe this shirt with so many details. You can visit mycubanstore.com and look for linen Guayaberas.
James Blunt - You're Beautiful
In the book the sea of monsters- where we meet Tyson- while they are having the "dodge ball" fight Percy has on shorts that have no pockets. So he doesn't have riptide- he left it in the pockets of his pants. When he goes and gets it it is still there. So riptide would appear in the pair of pants he had it in last that had pockets. So he's wearing jeans with pockets and he changes into shorts and loses riptide it would go back to his jean (unless his shirt had a pocket and then it would appear there.) Hope this is helpful :)
There are several types of pockets Patch Pockets Unlined Self-Lined Lined Side Seam Pockets Welt Pockets Single Welt Pockets Double - Welt Pockets Welt Pockets with Flap Side Front Slanted Pockets In-Seam Pockets