I first learned about packing cubes from
SmallNotebook.org. We have been traveling lately and found them to be very useful.
I bought my packing cubes from
Container Store for $10 each. I thought of ordering from Amazon.com but so glad I didn't because after comparing the different sizes and shapes, I decided to go with these cubes below { they were supposed to be for shoes, at least that's what the label says, but I found them to be perfect for Max and Wes' clothes}. So I got two of them that way their clothes don't get lost in the big luggage. When we arrive at the hotel, I just put those cubes in the dresser.
I use the same idea: using small compartments for my underwear and other small stuffs: