It is always optimal to do the full colon cleanse with both the IFs but if you feel like you can't do the IF2 while traveling then you'll be okay on just the IF1.
When Dr. Christopher made up the bowel formula it was just the one part, he never made the IF2 so thousands of people have used just the one. Things weren't as toxic when Dr. Christopher was in practice as they are now.
Just be sure to eat plenty of fiber and drink lots of water daily, lots of apples would be good.