A great tip from Lee Hutchinson at Ars Technica:
If you can keep your cable modem, router, and Wi-Fi online when the power goes out, you’ll almost always find that your ISP is also online—and you’ll keep your Internet access.
A few weeks back my power flickered. It was off for shorter than five seconds, maybe even shorter than two seconds. I have an uninterruptible power supply attached to my iMac, so I saw no ill effects on my computer screen—but the cable modem and router in the other room went down, so my network disappeared.
I bought a second UPS and attached it to those boxes, so the next time my power goes down, my internet will remain intact. I can still do work on my iMac with my network down, but it’s better if the network’s still around, too!