I don't recommend storing the crostini once they're fully prepped, but you can definitely store the ingredients separately and simply assemble when you need them! The cooked steak can be refrigerated in a sealed container for up to 3-4 days and the crostini can be stored in a sealed bag or container for up to 5 days. If you need to store them for longer, simply allow the steak to cool, place both the steak and crostini into separate airtight containers, and freeze for up to 3 months. Frozen steak should be thawed in the refrigerator overnight and then reheated in a pan for about 1 minute on the stovetop. Frozen crostini can be reheated at 400 degrees for 10 minutes and do not need to be thawed first.