I worry a lot about power outages because I'm from a cold climate, so I keep a bunch of 40hr heat packs handy just in case. If I see the temperature falling close to 75 in the room, then I crack a few (1-2 per cage) and stick them under the enclosure on the side where the snake is. I say under the enclosure though because I've seen those heat packs get up to 165F! So I just stick them underneath and hope the power comes back soon.
Another thing I do is rotate the snakes through a bit of handling or I'll put on a hoodie and let them sit in there for a bit to warm up a little too.