Depending on anticipated temps, in ascending order:

JRB Shenandoah quilt.

Cheapie fleece sleeping bag.

Silk or cotton liner.

......or any combination of the above.

Sometimes in the desert.....nothing at all, including clothing. It's just too hot when the lows are high 80's.

I found that quilts are very versatile for warm weather. They can be ventilated at night and then drawn tight to ward off the morning chill.
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If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.