I recommend the featherweight, if you can find one. A few weeks ago, my husband had to go somewhere on business, so I went along, taking my featherweight and fabric to keep me occupied while he was in meetings. Worked GREAT.
I can also recommend a Singer 301. Some call it the featherweight's "big sister." It's a full size machine, but made of aluminum, so it's lighter than a cast iron machine would be. Got mine at a garage sale for $20. It's an awesome machine.
However, if traveling for more than a few days, I'd probably have to take my embroidery machine as well.