Laufey: if you don't have storm shutters, criss-cross duct tape on the windows. They are a bit less likely to break, and it slows down flying glass. If your house has inner rooms not directly exposed to the outside, stay there. Keep a lamp or candles, matches and a battery torch close, a battery radio if you have one, plus food and water. Be very careful with the fire, both not to ignite your stuff and not to asphyxiate yourself. Probably sounds silly to worry about water in Iceland, but if you can't get to a room with a tap it can be a problem. First aid kit is a good idea too, and, gross as it sounds, a closeable container you can use for toilet purposes, and toilet paper, if your safe room isn't the bathroom (says the person who has ridden out several Qeensland and Northern Territory cyclones in solid bathrooms).
Keep with you your important papers (ID, drivers licence, medical data and prescriptions, contact list and the like), and a supply of necessary medications. A small tool kit. Warm clothes, blankets and quilts and pillows. Make sure all your devices are charged while you still have electricity, and if you have a powered charger keep it with you. Something to do (knitting, a book to read if you have light, a big notebook and pencils). Build a blanket fort and get some rest. And best of good luck!
Haiz, SectoBoss and anyone else sitting exams: best of luck! Sometimes you do better if you just relax and go for it as if you were writing a story. I'm probably not the best person to advise, because I generally enjoyed exams (except for the ones that required any kind of technical drawings, those were a horror and a nightmare). But all my younger siblings were nervous about exams, and they found the best thing to do was to read over your material several times, a day or so apart, rather than trying to concentrate intensely once, then to try for a decent sleep the night before, and to get up early on exam day, eat lightly, then go out and be active for an hour or so before the exam, go for a walk or something, to get the blood flowing and let the brain wake up. Courage and luck!