When you cook on a barbecue, which takes a lot of charcoal, put all of the meal items on so you don't use two sources of fuel for one meal. There is a way to cook anything on a barbecue. You can even put a can of beans on the grill as is.
Before the coals are hot enough to cook on, you could be getting a large pan or two of water warm enough for bathing. And, you can boil water after your meal is done cooking since the coals stay hot for a long time.
Large juice cans are great for safely storing ashes from the fireplace or barbecue. Any empty can would be a safe receptacle for the used matches. An empty milk carton is much safer for disposal of broken glass than a plastic bag.
Burn your candles inside empty tuna cans. The can will catch all the wax drips. You can light the candle before putting it into the can, tip the candle so the top is over the can, and use the melted wax to hold even the tallest candle steady. After using a can as a candle holder over and over, you will can turn the melted wax in the can into a new candle by adding a wick. Or, you can pop cooled wax out of the can and use it as a fire starter for the fireplace, along with clean trash paper.
Put some sort of container underneath the tap of a cooler to catch any dripping water. Have a dishpan underneath when rinsing shampoo from your hair to catch the rinse water. All of this water can be used to flush your toilet. Water from boiling food can be used to water your vegetable garden, after it has cooled, if you didn't put much salt in the water. Try a touch of oil instead of salt for boiling spaghetti. If you have ears of corn instead of canned corn, adding sugar to the water instead of salt not only keeps the water usable for plants but also makes the corn taste really nice. Not many of us will have ears of corn, and, if you do, you may want to save on water and cook the corn on the grill instead. Simply wrap it in foil and turn it often during cooking.
Used water or any liquid can be used to flush the house toilet, even if the water supply is off. You just need to pour in enough at one time - half a bucket full or a large bowl full.
Use disposable aluminum cooking pans so you don't have to waste water washing them. Or, line your cooking pans with aluminum foil so you won't have to use precious water to wash them. If you do get food cooked onto a pan, add a little water to the pan, then boil the water to unstick the food.
Lots of paper napkins will only be used to wipe crumbs from your face or hands. Paper goods like this can be put into a separate container and used to start your campfire later. Some paper plates will also burn nicely, but those with a waxy or plastic covering should not be burned. Burning all the safe and relatively clean paper items will also save on trash bags later.
Fry up bacon in a pan, then cook your eggs in the bacon grease. This makes the eggs look dirty but very tasty, and you are left with one less pan to wash. Boil eggs in the same pot when you cook pasta or potatoes, but wash the eggs first.
Get inventive, put on your thinking caps, and try to imagine some second use for everything.
EFFICIENCY IN ADVANCE
You may not be able to keep your car's gas tank full at all times, but this is not the time to get too close to empty. And, you should have extra gasoline stored in a safe container in a safe place.
And, now is certainly not the time to say you can't afford to stock up. Can you afford not to? Sell something, have a garage sale, or borrow the money. If you don't have enough money to buy a barbecue or a camp stove, and you have no where to make a campfire, then at least stock up on peanut butter and crackers. If you can't afford to go out and buy bottled water, ask all your neighbors to save some empty two-liter bottles for you so you can make your own bottled water. If you can't even afford the luxury of candles or flashlights and batteries, you'll probably survive. But, you can't survive long without food and water.