I had the same problem with overpacking. I now have a small sewing basket that I keep packed just for traveling to classes, etc. I supplied it mostly from duplicate items that had found their way into my sewing room. In it I have:
1 dark and 1 light marking pen/pencil
a seam ripper
scissors
tweezers
stiletto (spelling?)
extra bobbins
extra needles
neutral light and dark thread
rotary cutter and extra blade
pins
pressing and appliqué cloth
Then I put my machine, feet, cord, foot pedal, small iron, ironing pad, cutting mat, ruler and project into my rolling machine case and I am ready to go. If I were going for overnight I guess I would include my toothbrush and some clean underwear...