Best times to cold approach

So I get the train to work everyday and am always catching eyes with girls who will give a smile or try sit near me on the train and I think this would be a perfect opportunity to approach but I never do because I’m carrying a laptop and paperwork most the time so would feel strange then approaching a girl. I only feel okay cold approaching when I’m out casually or with friends. Am I correct in thinking this or just being stupid?

Beg for stats.