1- i use silk liner too, +/- $15 usd (eBay), and can add about 10 deg F comfort
2- i always carry a "space blanket". it has worked very well, but holds moisture with heat
3- i have a sleeping bag outer shell making 3 season bag to 4 season (different topic :-)

the silk liner is good during warm summer rides too, used on top of sleep-bag, and an easy wash!

stay comfortable!
t