Often I have had some cold days and night on the trail. These are some things I did to keep/stay warm.

If you have bad circulation extremities get cold fast. You might think tightening your boot will make you warmer but it will block blood. Make sure your arch has plenty of room to get warm blood to your toes.

Put your sock liners under your pants layer and your sock over, it will make a seal that will keep out snow/wind.

Wearing your rain pants over your hiking pants will really help contain heat.

Putting your next days cloths in your sleeping bag will have them warm to put on in the morning and help avoid the shock of leaving your sleeping bag half dressed. Even sleep in those cloths maybe.

You can also use tomorrows cloths to make a pillow. Pack a shirt or jacket and sleep on it.

Look at my face mask post for some make shift ski-mask options

Socks make great quick mittens, if you have ones to spare you can cut finger holes

Warming large rocks by the fire that can be later placed near/under your sleeping area can provide extra warmth to help you fall asleep

If you really need, find a buddy! Sharing warmth is a great way to stay warm, most cases of hypothermia occur over 50 degrees so be mindful

Wet = Cold, if you have to many layers, shed some so your sweat doesn't cool you later

Snow shelters can really help but make sure to dig a second lower level for the cool air to pool

Try to get out of the wind, rocks, trees, earth, anything to block it

Warm food = warm you, even allowing your water to warm in your pocket will help a lot