Stores, banks, post offices and businesses are closed on the following French national holidays:
Boulangeries and flower shops are usually open the morning of national holidays but everything else is closed. Except for Christmas day, it's wise to avoid travel if possible on a national holiday. The airports are a mess, roads are clogged, train stations are crowded. For warm weather holidays, everyone heads to the coast. Winter holidays sees everyone grabbing their skis and heading to the slopes.
And it's not just the holiday itself to beware! French people love to faire le pont or "make the bridge" which means that shops, restaurants and business will be closed on Monday if the holiday falls on Tuesday or Thursday if the holiday falls on on Friday. Some think: "The heck with it. Let's just take the whole week off!"