Last year, DH and I went camping in early October with our 40-degree bags. I'll admit that we were somewhat novice campers, and I didn't appreciate that the bags are probably only good to 50 degrees. Well, the temperature overnight dropped about 10 degrees colder than anticipated on top of that. It was a very long night, even with a lot of layers, hats and gloves. We now have true winter bags, in addition to our summer bags. Given when we do most of our camping--mid summer and fall--I'm hoping the bags will cover us. When it's truly hot out, we usually bring bag liners, too.

My advice is to bring more layers/blankets than you think you'll need for fall or early spring camping, just in case it turns colder than forecast. Bring a hat and gloves, too.