I always travel with a small paint kit. It includes good watercolor paper, paint, a small plastic palette and a tin pencil case with pencil, ink pen and 3 brushes. All together it takes about as much room as a medium sized book.
I love the quiet act of painting, however there is more to painting while traveling or anywhere in public. I frequently make unique connections with people when I sit and paint in their world. Sometimes people sit with me or stand over me for long stretches. Sometimes we talk, but more often we just smile and gesture. I also share paper and a few colored pencils with children who sit with me. Some of my more memorable experiences have been doing art with kids at Angkor Watt in Cambodia (some Korean tourists came along and we got our photos taken about a hundred times) and on a boat going up the Mekong river in Laos.