You can use the pickling spice packet that comes with your brisket, or you can buy a pre-made mix from the grocery store. It’s often more convenient to use one that is already made for you, and I like to save time where I can! You can make your own spice if you prefer. Feel free to add your own mix of spices, but the ones you probably want to include are mustard seeds, black peppercorns, and crushed bay leaves.  From there, you can add a selection of your favorite spices such as coriander seeds, dill seed, allspice berries, red pepper flakes, ground ginger, cloves, or cinnamon.  Experiment until you find a blend that you love!