Apparently the less you carry onto the airplane, the less it takes to power the plane, the less CO2 is blown into the air. So, don't pack a lot. If possible, a carry-on is the way to go.
I was also reading a book that said a way to impress a guy is to not have a lot of luggage as you travel. Guys don't, and they don't want to carry your fifteen pair of shoes for the two days. So, if possible, use a carry-on only.
So what do I do? Well, I think that checking in a bag is a waste of time. Such a huge waste of time and personal energy. So, I only take a carry-on. I'm still in search of the perfect boxy bag that is pretty small, and very inexpensive.
In my latest trip to New York there were nine guys, and one other girl. I was slightly proud of the fact that my bag was in the bottom four in size. Plus, I had extra room in my bag, which I was considering renting out to some of my travel buddies. It worked out quite well, never having to check anything, and was not a huge bother hauling around New York.
So, saving the world while impressing the guys..... Definitely going to keep doing this.