There are charts ad infinitum that will give you the amounts of layers of sandbags that are needed to stop a bullet, depending on the caliber. Most fill them with sand; however, unless you live on a beach, sand may be something not found out in your backyard. You can fill them with dirt, but the stopping factor is significantly reduced. It’s up to you: your decision (to paraphrase “Alice in Chains”). You can make them permanent with concrete. You can convert a front porch into a semi-fortified fighting position with three layers of sandbags about 3 to 4 feet high.
One of the big problems is that it’s hard (or impossible) to “scrap” different types of building materials or construction supplies out of the dump. The days of “dumpster diving” for materials are just about over. Salvage companies save everything to sell back to China, to be sent back (and sold) to us…as the salvors are raising money that is taxed by the local government…the same local government that will not permit you the citizen to “dumpster dive,” as it cuts into the “chain of events” just outlined…and their profits.
You’ll have to pick up some rolls of heavy-gauge fencing wire to cover over your windows. Nail them right to the frame with fencing staples, and ensure they’re taut. In this way, the Molotov will not go through. Also, ensure that you have at least 1 inch between this fencing-grating and the glass from the window. The Molotov may hit and allow the glass to break by bending the wire in enough so that the bottle’s weight impacts the window. Then you’ll have to cover the busted window with plastic.
And since we’re on the subject, you can pick up rolls of 6 mil plastic, 25’ x 10’ for about $10 at Wal-Mart…could come in handy to close those windows if needed. If you pick up the fencing wire rolls with rectangular apertures, say 2” x 4” it will facilitate you using the window as a firing port if the window is able to be opened from the inside and not a fixed window. I wrote several articles a couple of years ago for SHTFplan  detailing how to harden your home; I highly recommend reading them if possible.
A good door brace (also referred to as a New York Lock) for the entry doors to your home will help out. It won’t completely prevent a break-in, but it’ll slow it down enough for you to deal with it. Consider a good brace-bar to go across the door. You want to make sure you have a solid frame. If it is one of those premade “cookie-cutter home” frames, you may have to reinforce it.
Plywood sheets should be measured and cut for the event (or eventuality, depending on your viewpoint) that your windows will disappear. Cut out your sizes to be able to nail or bolt into the frame on the outside of the window, and mark the pieces to enable you to match them up to the appropriate window. I suggest (at a minimum) ½” pressure-treated plywood. Also: measure and match up with those pieces pre-cut 2” x 4” sections, to put together as a “T” or multiple “T’s” to brace up the plywood in the center when it is in place. You never know when some fool will try to smash out the center of the plywood and enter the house.
Cut apertures for firing ports and viewing ports at the appropriate levels in your sheets. You can cover these up with pieces of plywood either on a screw or on a hinge to the side, to enable you to use your firearms to deal with Mr. Moron who just won’t take “no” for an answer. Make sure you take down and remove any trees, bushes, or anything that can provide marauders with cover and/or concealment. Cut down these things and use them for firewood later.
Now is the time to place any building materials and supplies you can on your property for use in repairs later. Most of this article applies to those who live in a house, and it has not yet taken into consideration the plethora of neighbors, neighborhood associations, and other assorted worthless groups that try to infringe on your rights and safety in the interest of keeping their property values high and in conformity. You may have to do it all on the q-t, and keep the OPSEC at a high.
The best thing you can do: conduct a thorough assessment of your home and determine likely avenues of approach for invaders foreign or domestic, weak points in the house, and areas where you would most likely make a stand. We’re getting “long in the tooth,” so to speak, with world events, and you need to harden all of the points of your home now while there is still time. An ounce of prevention is more than a pound of cure. Keep fighting that good fight! JJ out!