Keep leftover Balsamic Brussels Sprouts in an airtight container for up to three days. Brussels sprouts can get overly soft and let off a sulfurous aroma when they are reheated in the oven, so I don't recommend roasting them and then reheating that way. Instead, quickly rewarming them in the microwave only until they are steaming hot is a great way to make them ahead. You can also prep them in advance by trimming and cutting them in half. That way they can easily be tossed together and roasted in no time.