If it works for eggs.

Through my childhood and teenage years I had a bunk-bed to myself. I would sleep on the top bunk and use the bottom for storage, occasionally switching which bed had which purpose. The storage bunk had an egg-shell type of mattress topper, and I would store my souvenirs, knick-knacks, and miscellaneous items in individual depressions forming a grid. That is how I kept my stuff ordered and things where I could find them. I was probably using it as an auxiliary brain (like I use my phone these days) and storing items was the equivalent of storing things in my memories, I'd, merely have to look at or touch an item to bring back memories.