For the person who wants a plan B for shelter that does not consist of a tent or sleeping under a tarp, a survival retreat is a must-have. Survival retreats do not have to be expensive either. Hunting land can be had pretty cheap and small cabins can be built with the surrounding trees if you have the expertise.
I have compiled a small list of things to consider when looking for a safe place to flee.
Distance From Home
Typically, you will want your emergency shelter to be within a gas tank trip. For most vehicles, that's no more than 400-500 miles. Not knowing what kind of disaster you'll be fleeing, you will want to be able to get there quickly. If you live in Indiana, a retreat in Utah will be pretty pointless.
Distance From Civilization
The point of an emergency shelter is to get away from everyone else. As supplies dwindle, people will turn to violence and you do not want any part of that desperation. I would suggest you look for property that is at least 100 miles away from a major highway and at least 300 miles from a major city. As society begins to collapse and supplies run short, everyone will be making their way to the country. The farther away from civilization you are, the less chance you have of anyone finding your retreat and attacking it.
Access to Fresh Water
Everyone knows how important water is for your survival so make sure you have fresh water close by. Either a fresh spring or flowing water is a necessity. Make sure access is fairly simple also, like a manual pump.
Plentiful Natural Resources
How much firewood will you need to cook and keep your family warm? Is there space for a garden? What types of animals frequent the area? It is also nice if there are natural choke points, high points and other factors which can assist in defending your home. Plan on being discovered and needing to protect your home from desperate folks.
Secrecy
The last factor is keeping your emergency plans secret, from everyone. The best retreat is one no one knows exists. When looking at properties, make sure no one knows what you are doing. If you are dealing with an agent or a bank, they do not need to know your plans. If you are building a new shelter, try and use very few contractors and just explain it as a hunting cabin. The last thing you want to happen during an emergency is to arrive at your retreat to find the real estate agent has already taken residence and is using your supplies. A person willing to take your property, is also willing to take your life to keep it.
I hope these points help and please feel free to add some factors you think I missed in the comments.
Keep on prepping!