Although I have a large spice rack, I have a designated mise en place area for ingredients I use all the time. This includes seasonings like salt and pepper as well as my favorite spice, cumin. While we never cooked with it growing up — my mother hates the smell of it — I have grown to love it, and now I don't think I could live without it. It lends a certain earthy smokiness that no other spice can add, and I put it in everything from Indian-inspired salsas to house pickles.
What spice is indispensable to you?