I can understand wanting to pack really light if you are doing a lot of solo travel (when I was 21 I traveled Europe for 8 weeks with a duffel bag!) But I'm wondering why this is necessary on a ABD tour. How often will you be traveling with luggage - isn't all the luggage dealt with for you?
ABD only allows one piece of luggage and a carry on. So you are kind of forced to pack light anyway.
Is this absolute? We are staying in Europe another 9 days (Rhine River Cruise) after Viva Italia and I was intending to bring another small piece of luggage with some nicer clothes. I guess I'll have to call them.
There are other threads that discuss the number of bags you have, and it looks as if they will handle your bags without issue even if there are a couple extra for your group.
If you ask ahead of time though, it looks like they tend to stick to the 1 bag rule.