For short trips I check the weather forecast, for longer trips I prepare for worst possible conditions.

In winter I add down jacket, short down pants, shoes with vapour barrier, warmer gloves in 3 layers, balaclava, extra wool underwear shirt, warm sleeping bag.

Cotton shell is great when its cold and dry, awful when it's warm and wet. I have not used wool shell much but I gueas it works fine in cold temps with low activity.

For solo day trips I bring a elephant foot down bag in case of an unplanned stay.