My save I shared here last Saturday has everything unlocked, weapons and outfits. I'll share it again below.
Just played the boss fight, my save does indeed have all the weapons and outfits unlocked. Unless you unlock something from killing the boss. Also, far as I could tell, the RPG is not in the boss level.
Speaking of the boss, I must be missing something. I shot the little cabbage monsters, until he showed his eyes. Then, I shot his eyes, over and over. At least five shotgun blasts went in his glowing eyes. Nothing happened, he just kept roaring and sending more angry cabbages after me. Then, he just ate me. Even though I was on the other side of the room, he's apparently allowed to one-shot you whenever he feels like it. I feel as if this boss was designed for the sadists who get off on having their ass beat by a mad Cabbage patch kid.
Here's my save again. All outfits and weapons.