You need to start thinking ahead now. Get the garden started now, don't want until you have to bug in to try planting seeds. Same with catching water, get a tank and put it under your porch/deck and get the gutters plumbed in to it now. Look into grey water recycling inside the house, a tank in the basement/crawlspace that the shower and washer feeds into to use for flushing the toilet.
if the family is going to be gone you can test, shut off the power, water, gas, etc and see how long you last.