It’s almost a cliché — stores sell out of toilet paper and milk before the big storms hit. The panic buying may make for punch lines, but people do have the right instincts. A bad storm not only can leave you snowed in, but it can disrupt the supply chain, leaving shelves empty even after the streets have been cleared and the power has been restored.

The Federal Emergency Management Agency has some practical advice for how to prepare for the big storms:

Water: Big power failures can disrupt your water supply if pumps aren’t running, and flooding can foul the water supply. Every household should have plenty of clean drinking water on hand at all times. The rule of thumb is three-quarters of a gallon per person per day — that’s three quarts, or liters if you’re metric. It also doesn’t hurt to have extra clean water for washing and food preparation. And a gallon container of water will flush your toilet if the water is shut off.

Food. Always have at least three days’ worth of non-perishable food on hand. It won’t do you any good if it has to be refrigerated and the power goes out for a week, so make sure to have crackers, dry cereal, pop-open cans of food, shelf-stable juice or milk, soup, etc. on hand. Keep a non-electric can opener in a drawer. Don’t forget basic needs for pets and small children.

Flashlights. Have plenty and make sure the batteries are fresh. A hand-cranked flashlight will work forever, even after batteries run out. People were without power for weeks and even months after Superstorm Sandy hit the Northeast in 2012 and after Hurricane Katrina in 2005.

Power. Do you have a generator? Be prepared to go without electricity for several days, at least. If you have electric-only heat, how will you keep your home warm? Many gas-heated homes need electricity, too. Many gas furnaces have electric pilot lights, and HVAC systems need electricity to push air. Using a barbecue or even a gas stove for heat can prove deadly — both create carbon monoxide fumes. The single biggest cause of death during power failures in the U.S. is carbon monoxide poisoning. Most cases are of people who didn’t realize that bringing an outdoor barbecue inside is a deadly mistake. Even keeping it just outside a door can allow deadly fumes to come inside.