Each day there will be one shipwreck somewhere on the beaches of San Andreas. The reward for finding them is GTA$ 20,000, 2,000 RP, and one Outfit Scrap.
Read this article to find out where to find out how.
How to Find the Daily Shipwreck
Each day there is one shipwreck spawned randomly in one of 30 locations (see the map below for all 30 locations). All you have to do is head to each spot and see what you find.
When you get close to the shipwreck you'll hear bell sounds and feel controller vibrations, similar to the Treasure Hunt.
As you may have seen from the picture above, these are more like rowboat wrecks than actual shipwrecks so they can be a little difficult to see from far away.
Because all the shipwrecks are located on land but at the water's edge, you can search for them with land, air, or water vehicles. If you do the Daily Hidden Caches, this would be a good time to also search for the shipwrecks.
How to Unlock the Frontier Outfit
Each day you find a shipwreck you will also receive one Outfit Scrap. When you collect all 7 you will unlock the Frontier Outfit. That's all there is to it. Happy hunting!