Use 'bundle up' when advising someone to wear enough in cold climates to prevent feeling chilly. The forecast says it'll snow later, so bundle up well.
Pro Tip 2/3
Care Concern
Shows care for another's comfort or health in cold conditions when used in conversation. I don't want you catching a cold—make sure you bundle up.
Pro Tip 3/3
Not Just Coats
Refers not only to coats but any winter gear, like hats, gloves, and scarves. Mom bundled up the kids with hats and mittens before school.