Brandruff

The powdery remnants of breakfast cereal found in the bottom of the cereal box, which falls from the bottom of the internal polythene bag all over the last few whole pieces of cereal you managed to shake out, creating the appearance of a form of gastronomic dandruff upon your morning meal. Originating from, though not limited to, bran-based cereals.
British colloquial term for Cereal Dust.

Alan, did you remember to buy anymore Shreddies? This packs nearly empty - it's mostly brandruff left.

I tried to be careful while pouring out the Cheerios, but they still got covered in brandruff.

brandruff

Dandruff caused by using an offbrand hair product.

Damn! That dollar store shampoo gave me brandruff again. I should have used Patene; now my head is itchy.