There are two schools of thought on traveling thread. One says that you should take your complete spool collection, so that the colors can be matched perfectly. Another says take one universal color which blends well, and leave all other threads at home. I tend to estimate which fabrics I will be using and take along all silk thread colors to match. Just in case I have forgotten a color, I also like to include the "universal" thread. I also include one 60-weight cotton thread to use for quick-basting the pieces to applique to the background.
This time I believe I may try taking my tiny spools, instead of the full size spools. Last year while wandering through the craft store, I saw some small spools measuring 10/16 of an inch by 7/16 of an inch. I purchased 32 of the little spools (translation: opportunities to take 32 colors of silk thread along on a trip). To keep the spools under control, I purchased a see-through plastic container 4 1/2 inches by 1 and 3/4 inches which had 4 screw on compartments, each holding 8 spools. The size and weight make it possible to carry the thread in one's carry on luggage. Just to be on the safe side, I will take a regular size spool of the universal color silk thread (YLI silk thread #235. Thanks, Stella, for this information) and one spool of 60 weight basting thread to supplement. The capacity of the small spools is rather deceptive. When one is dealing with silk thread, the small spools hold several yards of thread. If one uses 60-weight cotton thread, the small spools still hold an adequate amount of thread for one 3-week trip. I plan to include a photo of the spools for comparison.
In an earlier life, I was a backpacker and hiked the mountains of California. I was always looking for ways to miniaturize things so that I did not overpack, and thereby unnecessarily increase weight. Since airlines are very weight conscious, I believe we need to start thinking like a backpacker.