seriously though; i spend a great amount of time commuting around, so i do my best to get the practice i can. anytime i've found myself waiting around after work, in between plans or just supplies to have on me away from my desk, the ones listed have led me to keep strong lines and necessary details during drafting studies. some stay in the moleskin, and some are so tight, they are ready to be transferred over once i get back home to final inks.
i didn't add this to the list, but for a pop of color, i H I G H L Y recommend winsor and newton's 12 color water color set. it's convenient to squeeze into a backpocket or small purse. i find myself carrying water bottle caps i've washed out, and pouring out of my water bottle as a mobile water dish for painting.
other suggestion would be one or two COPIC or TOMBOW dual markers for a pop of color/ shading, ONLY if you want color and DO NOT give the watercolors a shot.
lastly, best sketchbook to use is anything really. i draw small scale and find myself incorporating water colors or heavy inks, so the moleskin watercolor pad has benefited me majorly over the years. i'm obviously someone who doesn't rely on expensive art supplies to get where i want in my illustrations.
the list i've made is to accommodate to travel and drafting what you can when the time you have to sketch is TBD. stay light, only take what you need so you're not stuck breaking your back with a whole assortment of paints and brushes, spilling ink in your pocket, or losing expensive pens.
also, thanks to TIME WARP in CEDAR GROVE for offering a great selection of comics to grab after work today.