If you have a small tent, put it up and insulate with blankets, mattresses, drapes, rugs, rug foam etc. For two people, one ideas is to crawl between two mattresses and pack the edges. If possible, add additional insulation to walls and exterior doors and windows with slabs of Styrofoam. If not, plug up air leaks with newspapers or whatever you've got. Buy spring water or put water away in food-grade containers or both.
Most supermarkets sell spring water in large plastic bottles.
One thing to know is that the plastic of these bottles will occasionally give out, especially if you have them around for several months. Keep checking them and store them, if possible, in a place where a leak will not mean a lot of problems. If they are in a location which is likely to freeze if the heating goes off, pour off approximately two inches or a little more into a new bottle, giving room for it to freeze and not break the bottle or split the plastic. 16 drops of bleach per gallon. Mix well and let stand for 30 minutes before use.