If kept stored separately yes, sausage gravy and biscuits keep well. Store the biscuits in a sealed bag and keep them on the countertop for up to 3 days. The gravy should be cooled first, then transferred to a sealed container, and kept in the fridge for 3-4 days. Reheat the biscuits in the microwave for a few seconds. Reheat the gravy on the stovetop, and add a splash of milk if needed to thin it out a bit.