bkt has indicated sandbags as he has flooding issues from time to time. That makes sense for his location. Now sand bags aren't going to keep someone determined to get in, out of his property, but it could slow them down.
Baring the windows with plywood, especially from the inside where you brace them against the studs in the walls with cross braces as dog2000tj has indicated is smart. You still loose all your glass to whatever natural disaster or man made eff-up that is coming, but at least you retain SOME control over the plywood cover. If you nail it to the outside, you can hook a couple of corners with mule tape, hook the other end to the back of a 4x4 and rip it right off.
At least with the plywood inside and mounted to 2x4 cross members that are anchored to wall studs, you remain some control.
Now my place has an oversized generator plumbed to the natural gas line, so it's running as long as the automated gas delivery system is working. That means I have power for lights, lots of them, including portable ones that can be turned on, off, aimed and turned back on to blind would be assailants.
We have the benefit of two German Sheppards that seem to treat this house and our yard as their personal castle. Even the mail and UPS folks have stopped ringing the doorbell and just place deliveries at the entrance to the walkway in/next to/behind the potted plant.
180,000 scent receptors will go a long ways towards telling you about trouble before you know it's there. Factor in the super sensitive hearing and you have an excellent early warning system.
I think you need to evaluate what you have, and what you would do if you wanted to get into the area you are living. How would you approach it? What would you do first in recon, or in trying to infiltrate?
Work backwards from there on your defenses. Use what you see as a weakness in an approach and make it a strength on defense.
One of the coolest things I have seen first hand was at a house of a normal "back up" band musician's home here in the Seattle area. Guy was a jazz musician with some skill, but worked pretty much as a fill in band back up. Made decent money, but was cool and had a service call on the cable at his house that I was lucky enough to catch.
I show up and the guy has an EPIC Koi fish pond between the unattached garage and the entrance to the house. Like three bridges, but only one was straight from the parking area to the front door, the other two circled the pond like a peace symbol.
I'm walking up to the front door, on the straight, obvious pass and about two steps in there were 3 boards that were linked together and when you stepped on them, they completed a circuit and the pond light up, the doorbell went off and then about 5 flood lights kicked on. It caught me COMPLETELY off guard... LOL
It was a great set up, super easy to replicate, and totally effective if you aren't expecting it.
I think creative home defense is only limited by your own imagination.