What are the Dead Ghosts for

Golden Chests just contain loot, yes. It's also worth noting that they scale on the area, not your level. So it's best to find them asap. You also are given an item for finding all the golden chests on a single planet. I know that you get a Sparrow from Earth and an Emblem from the Moon.

There's a few on each of the planets in-game at the moment. There are 5 on the moon

1 - Found during the The World’s Grave mission inside the cave full of cocoons.

2 - Head to the mission marker located in the large yellow building. Proceed until you find the green gas pit. Look nearby for a rock formation and orange lights.

3 - Another in The World’s Grave. When defending your Ghost search a nearby room with a little pool of water

4 - Inside the Temple of Crota during the Chamber of Night mission.

5 - The Summoning Pits Strike mission. After the final boss fight walk to the edge of the room and drop down onto a small platform

I'm affiliated with Gamers Heroes and we have a guide on the topic should you need more direction: Destiny Gold Chests Moon

Some of the materials are used to upgrade blue and higher gear. Some of them (the ones you collect from resource nodes on patrols) are used for upgrading purple or higher gear, but can also be traded in for crucible and vanguard rank and marks.

There are also some quest lines that use some of the various things, including consumables, for exotic gear (yellow level, above purple).

There are also a few different kinds of currency that show up in your inventory, mainly strange coins and motes of light. You'll use those later in the game to get high end gear.