MDtR-Chicago and jcmitchell21 have both offered valuable advice. On a trip where you're likely to mix a number of airlines, you should know the most restrictive baggage rules that apply or else be prepared for some possibly nasty baggage fees. There is no universal agreement on what's a "carryon" and what has to be checked. There's also no agreement about whether you can bring a carryon and a personal item. You need to know all of the baggage rules before devising a packing strategy.

And jcmitchell21 is spot on about a key packing strategy--reducing the amount of packing you do so that you can avoid checking bags. On an itinerary where you're likely to take a number of different flights, you increase the likelihood of lost baggage. You'll also increase your airport time by 30-60 minutes per destination waiting for your checked bag to reach the baggage claim. Other than my golf bag, I haven't checked a bag in years--and if the airlines would allow me to bring those onboard, I wouldn't check those either. Plus, hauling around heavy luggage gets more onerous the longer the trip. At some point during your trip, you're likely to be pretty angry about all the stuff you're carrying.

Yes, it's good to be prepared for all different types of weather, but I guarantee you, you'll probably not use 40% of what you pack. I now pack assuming I need no more than three days of clothes changes. That doesn't necessarily mean totally different clothes for each day--it generally means different shirts, sweaters (if needed), and tops that I use with two pairs of pants. One extra pair of shoes. More technical type clothing than I usually prefer (I'm a cotton and wool guy by nature) that is easily cleaned in a hotel room. A pared down toiletry kit (unless you're outside of cities in undeveloped parts of the world, you can buy toiletries or use those you find in hotels).

If you'd like to learn more about these ideas, I'd look at the Travel Products forum here at FT. The folks there are as obsessed with packing as much of the rest of FT is obsessed with accumulating miles and points.