Long Underwear
There will be times while you are on the trail that you will be cold. Having a set of long underwear or an insulated base layer is exactly what you will need to stay warm. You can also use your long underwear to sleep to double up on uses for clothing. Just make sure anytime you wear your long underwear outside of your sleeping bag you have clothing on top of it. Doing so will protect them from becoming smellables by food items touching them.
If you are going to use these as your sleeping clothes, store them inside of your sleeping bag. You can pull them out when you need them. Typically you will put them on in the evening when it starts cooling down and wear them until you wake up in the morning and break down camp.