Backpack
There is a handy backpack feature which acts as a quick access to certain weapons/pickups. To access the backpack move the controller out of sight over your shoulder. Press and hold one of the following buttons to access the associated items:
Dominant Hand Controller
A (or X for left handed) - Knife (useful to quickly smash up stuff or stab)
B (or Y for left handed) - Binoculars (once you have picked them up in game), raise them to your face to look through them, pull trigger to zoom in/out
Grip button - Grenades / Dynamite - You can then throw them in the usual manner using the trigger
Release the button to return to the previously active weapon
Off Hand Controller
X (or A for left handed) - Quick Save Game
Y (or B for left handed) - Load Last Quick Save