The players assisting you would be remnants of players who previously fought the boss and died, they throw you the gear they brought with them. If you died it’s possible your ghost will assist countless other players just like this in the future.
Yes cairns mark where players rest, and if you pee … Well you’ll see.
Everything you place, ladders, ropes, bridges etc, has the potential to appear in another player’s game and assist them, they can even leave a like so you know they used it.
You can also connect strands to other players whose stuff you’ve used and their stuff is more likely to show up going forward.
If you’ve lost any cargo down a deep valley or to a river current or just had to abandon it for safety, it will show up in another player’s game too and they can finish your delivery. You can find othe players lost cargo scattered in the wild where it was abandoned or stored at depots.
I love this non intrusive and helpful form of multiplayer. Feels very communal despite never physically interacting with a single soul.
Kojima is always breaking the fourth wall.
In metal gear solid on PS1, a boss reads your memory card and comments on other games you’ve played, they also ask you to lay your controller on the ground to demonstrate their psychic power. The controller vibrates and begins to move across the floor. Clever use of what was a new technology for console gaming at the time.
At one point you’re even told to check a screenshot on the back of the box to get a phone number. We rented metal gear solid the first few weeks so we had to call the video store and ask them to check the box for us 
There’s lots of hidden Easter eggs in the resting room if you mess around with Sam and the camera. It’s definitely more overt this time, they have norman reedus make lots of eye contact with the player and do silly little things, it almost feels like it’s an extension of the actor reaching out to the player. Which fits in again with the games central theme on Connections or Strands.
They added a sunburn mechanic to the second game 
I was outside for way too long
