After a little trial and error, I've come to the conclusion that a very mini art kit is the way to go. Easy to pack and take with me anywhere. I fill my pen (this one's by Lamy) with ink, take a sketchbook, a small watercolour palette with 12 half pans, a water brush and a sketchbook. This works for short trips but may need to be adjusted for a bit longer (I'll probably need more ink) but I really like the simplicity of it so far as it encourages me to create on the go a bit more. I may have to include a smaller sketchbook and a small bottle of ink so that it fits into a smaller pack (like my waist pack) for a longer trip.