Far Cry 3 Items on map don't exist

I keep getting to map locations where the map indicates there are items but 60% of the items simply aren't there!

I go to a relic location and there is no relic to find, for example. I go to a box location and find no box.

Solution 1:

Sometimes you'll see an item on the map, stand exactly where it is, and won't see it. The truth is, it can be directly above or below you, maybe even inside a cave below the island.

The best way to see where an item is, is step a few meters back, open the map and set a custom marker on it. The custom marker will show up on your HUD as a rectangle and you can see if the item is on the same level as your are, above or below you.