In one word, DEET...

What clothing do you pack for a round the world trip, when your constraints are

• the number of luggage pieces you can check or carry onto flights and ships, and their capacities, maximum dimensions, and maximum weights
• the climates you will be visiting, the predicted temperatures (cool vs. hot) and rainfall, and the sun and mosquitoes you must protect against
• the need for clothing for more social occasions (the "dress-up" dinners) vs for climbing around temples (rugged, easy-clean, mosquito-proof) vs for city exploration (temperature-controlled, dry, foot-saving) vs for fun (quick-drying, sun-protecting)
• the cultures you will be visiting (conservative vs. Western dress)
• safety and security (protecting your money, identity, and important papers)

In our case, we anticipate at least three dress-up dinners on the trans-Atlantic cruise and one on the Nile cruise.  The Atlantic crossing and the cruise ports will probably be somewhere between chilly and merely cool.  The heat will begin in Egypt and build to hot and humid in Cambodia.

Clothing should be conservative to suit the cool temperatures before Egypt and the cultures encountered with Egypt and beyond.  The lighter clothing needed for the hotter climates should be sufficient for the cooler climates if worn in layers.  Our concession to the cold temperatures when we leave home is to wear thermal underwear and fleece parkas.  When they are not needed again, they will finish the trip in compression packing bags to minimize space used in our luggage. 

While rainfall should not be a problem (we are avoiding monsoon season in each country visited), we will have light rain jackets and a small umbrella. 

We are each bringing a hat to protect against sun and rain.

Our biggest concern has been mosquitoes and the diseases they carry.  We are each bringing several items of mosquito-deterring clothing ("bugsaway" and "insect shield") in addition to various lotions and sprays containing DEET. 

Shoes are always a problem. We will have three pairs each: one pair athletic shoes for exercising and for touring; one dressier pair for dressier occasions; and one pair of Tevas for beach and water activities.  We will wear the largest/heaviest pair for travel.

For the first time in traveling, we are seriously concerned about asset (and identity) theft.  We will use RFID protectors for our passports and credit cards.