Great information and advice, Paul!
Coldest I've camped was 28 F with frost on the outside of my MSR Hubba Hubba old tent. I have a 38F reasonably good sleeping bag bought from REI ten years ago, and a silk bag liner. It's worth mentioning the actual effectiveness of degrees advertised on a sleeping bag vary wildly depending on individual's physical condition, state of rest, health, etc. They are just ballpark numbers for being able to survive - not be comfortable.. Thick wool socks, beanie and good thermal clothing. But I could not close an eye all night due to cold. It wasn't fun at all. being tired almost ruined my next day. If I knew I am going to be exposed to such camping conditions, I'd buy the best gear there is. For occasional / accidental use, I'd just follow our advice above, and suck it up with the cold best I can. But if there's an option to get a room, I would not hesitate skipping camping.