Whenever I'm asked to paint live I like to work on a larger canvas (24-36 inches) so that it's easier for everyone to see what I'm doing. That means bringing along a larger travel easel and a larger 'tool' box. Here is a list of my favorite items to travel with:
2. paints (typically about 8 colours: ie. a red, blue, yellow, white, turquoise, lime, purple and magenta or alizarin)
3. a variety of brushes (foam & regular)
4. paint pens
5. mark-making tools: lids, palette knife, brayer, card
6. spray bottle
9. water dish (I've begun using a collapsible pet water dish)
I also bring along a nametag (which I usually forget to wear), a rag rug for under my easel (since my work tends to be a bit messy) and a camp stool (which I use as a table of sorts for my paint box). Finally, I try to remember to bring a small moleskin sketchbook, a water bottle and granola bar, and my camera.
Actually, now that I think about it, this is basically what I use in my studio as well, just a little more of it all.