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I haven't progressed very far, but so far it seems that those enticing "Golden chests" yield cards that you use in multiplayer, and in another game!

Does Thronebreaker, which is advertised as a single-player experience, have a lot of this kind of stuff? It really puts me off the game. Why go through the trouble of exploring stuff, if you just get stuff you can't use in the single-player campaign.

(Also, I seems to mostly get "Failed to unlock x" messages when opening those chests.)
This question / problem has been solved by Zulfurlubakimage
Probably have to disappoint you, but yes, all of the golden chests include rewards in form of premium cards, avatars and avatar borders for another, multiplayer card game Gwent. Every reward is tied to the specific golden chest and once it is unlocked (for example, on the second playthrough), golden chests will give you gold and/or wood.
Golden chests contain also gold and wood. Thronebreaker is kind of single-player expansion for Gwent, so it's obvious you'll get something for multiplayer.