Metal Gear Solid 3 reference
When Drebin and Little Grey jump off of the Stryker, they will land in Naked Snake's pose from Metal Gear Solid 3, when he first arrives for the Operation Virtuous mission.

Equip the Patriot gun to hear music from Metal Gear Solid 3: Snake Eater.

Press L1 to view the description for the Mosin-Nagant. It mentions The End and his sniper duel with Big Boss.