My favorite possible additions:

Banana! (has TONS of k)
Apple skins (PK)
cantaloupe rinds (PK)
coffee grinds (mainly N)
Lemon skins (more P actually! surprising as Grapefruit and oranges are mostly K!)
Molasses (K)
Orange rinds (K)
potato skins (p but BIG K)
Potatos in general, too (K)
Firepit ashes (K)

Note to self - things that can be used when we need certain ingredients. (common for my home, at least!)