My power just went out last night for about 12 hours, luckily I insulated the room real well when I built it and the lowest the temps got was 58. Mine were a little slumped over when we got power restored this morning but other than that it wasn't too bad. There isn't a lot you can do as far as light goes and so long as you don't have photoperiods in veg it really shouldn't matter much. An extra day or two without light won't kill them. The biggest concern should be temps. I don't know how big your space is but even a small kerosene lantern in there will keep the temps up pretty good. Like a hurricane lantern, you should be able to pick up for less than $10 and it wouldn't surprise me if it didn't add an extra 10 degrees to your grow room if it is completely closed off during the outage.
Best of luck!