Blizzard has explained how the open world weekly caches in War Within work, noting that they will be giving players more options!
TL;DR Instead of a pre-determined weekly activity, players will be tasked with completing their choice of various activities.
If it’s one of those first two caches earned that week, and The War Within Season 1 hasn’t yet begun, the cache will contain Adventurer gear. Once Season 1 begins, that gear will be Veteran gear, and the text will be updated to reflect that. We don’t want anyone to worry that outdoor players aren’t going to have regular sources of Veteran gear, but we also don’t want anyone to feel a need to play content they don’t want to play just to start the season with as many Veteran pieces as possible.
The first four caches you earn each week from any source (same list as above) will give you 100 Coffer Key Fragments, which can be immediately combined to get a Coffer Key for use in Bountiful Delves.
For the sake of brevity, there isn’t text explaining this on the cache items, but if the text mentions the first two having gear, this rule will apply as well. This “first four” rule isn’t in today’s build, but you’ll see it in the next one.
Please note that the contents of each cache are determined when you get the cache awarded to you, not when you open the cache. There’s no reason to hold onto them and open them later.