Let's assume you cook using a wood or coal fired oven. That could be a real wood stove (very good to have) or just a home built clay baking oven.
This is very applicable in a SHTF situation too, not just because I would really like to be able to cook on a wood-fired stove.
Without a thermometer, you will need a way to judge just how hot the oven is.
This article gives three time-tested temperature tests:
http://granny-miller.com/oven-temperature-testing/1) Flour in a cup, browning time
2) Hand-in-oven, 20 second test.
3) Scrap of paper browning times.
The article also gives these approximations, when you have an old recipe which does not use actual thermometer readings:
A Slow Oven: 250ºF. to 300ºF.
A Moderate Oven: 350ºF. to 400ºF.
Hot Oven: 400ºF. to 450ºF.
Very Hot Oven: 450º F.to 550ºF.