First, I pull out my super sturdy ArtFest bag from 2008. This bag is nearly indestructible, has plenty of room, and is washable. I also always bring a small camera and remember to pack it in its own travel hard-case, (so when you drop it you won't cry)that you can get at most camera stores...then just pack all your cables and cords separately in your suitcase. You won't need them to draw but you may use them later if you travel with your laptop. (I much prefer to leave the technology behind, personally)
Next, pick a small journal. I was recently introduced to the small Handbook journals and LOVE them. They are tough, and their paper is yummy, heavy and will take almost any medium. My friends and I got together at Kim's studio and made this great removable and reusable covers for our journals out of scrap fabric that was woven onto a rug-hook backing and stitched over and over again. Pretty, no?
Now, drawing supplies: Of course when I took this photo I forgot the most important thing, GLUE-STICK...put some Uhu-glue in there to stick down all your travel ephemera that you can draw on or around. Then pick the tools you most use while sketching. I use about 4 to five water-color pencils all the time, several point sizes of Pitt Pens, a few colors of brush Pitt Pens, and mechanical pencil and a good eraser. Add a small brush and you're ready. I put all my supplies in this great, sturdy, small pencil bag that comes with a hook closure to hook to your belt loops or outside your bag for easy access.
There, we're set to go. When I'm traveling I like to keep the supplies to a minimum...then you do much more drawing an having fun than packing and un-packing and re-packing again....and cursing all the while. Keep things simple and have fun!