I've been on the plan since mid-July and didn't substitute at all for the first month or so. Then I had a time where I had to go out to dinner and I just made sure I had something healthy - grilled chicken, salad, veggies - and it worked out fine.
One of the things I missed alot with joining JC is going out to dinner periodically with my best friend. We used it as a chance to talk and catch up on things and I really missed it. My JCC reviewed the guide in the back of the volumetrics book and also the eating out guide and reviewed some of the healthier choices I could make and it worked out fine. Not always easy - obviously - but I have continued to lose, so I guess I did okay.
I try not to do it too often because I don't want to derail myself.
Talk to your JCC - they're there to help you along this path, to make the right choices and make it as easy as possible to stay focused and on the plan. If you really want to eat some things with the family and are blaming the JC food that you can't - it might make you start to eat things you shouldn't and that would defeat your good intentions of joining JC.
Good luck.
