The 6 survival caches found in The Wicked Vale do not count towards this as they are technically DLC.
You need to find Explorer Satchels which will then put the Survival Caches on your map and allow you to loot them. I found the guide on IGN very useful as they show you where all the satchels are. Just in case you are having trouble locating them:
http://uk.ign.com/wikis/rise-of-the-tomb-raider/Explorer_Sat...