Shooting all 20 tokens gives you all perks for the rest of the game (even if downed)

paying 15000 at the radio next to electric cherry will teleport you to the boss room

defeating waves in the boss room will grant access to the gun room

Edit: shield parts. one is up on the pipes (near deadshot)

one is on the top of the tower.

one is next to pack a punch (that square before you actually get to pap)

<3