Great 3+ Season bag
This bag is super compact, light, and reasonably warm- making it ideal for spring, summer, fall, and warmer winter excursions. If you're bivying in a snow cave, I'd probably opt for a little bit better insulated bag, but if you're snow camping in a tent, it's generally pretty warm. I usually carry this bag, plus a bivy sac to add a few extra degrees of warmth. If you're regularly snow camping with ski boots, kick down for the extra long one so you can keep your liners in the bottom- allowing them to dry out a bit while you snooze.