Yes, there is the cafe at the top floor with a terrace and wonderful view of Palazzo Vecchio and the Duomo but the restaurant will be on the ground floor and provide a whole menu and chance to sit down and rest so it will be another experience! Unfortunately, it definitely won't be open that soon, so the Cafe is definitely your only option for a snack to stay in the museum as long as you like. If you exit, you cannot go back in.