Is there a way to prevent mixed cereals from separating?

I quite enjoy cereals that have a range of different ingredients - like oat clusters with freeze dried strawberry or museli with almonds and raisins. Over time though, the oats rise to the top and the smaller bits get trapped at the bottom so when you're near the end of the packet it's 70% dust.

Is there an easy way to prevent this? It's hard to mix up the contents without breaking up everything into smaller bits. And shaking up the packet just makes the separation worse.