A friend who is a flight attendant recommended these, and I'm glad she did! If you're a "my-suitcase-gets-disorganized-five-minutes-after-I-open-it" person like I am, these are for you. On a recent week-long trip across the country, these kept everything organized, separated, and relatively wrinkle-free. They also made unpacking at home (which I hate) pretty pain free.

*Size for different luggage types: I was able to get all four in a carry-on suitcase (just no room for the laundry bag--it was a snug fit). They of course fit in a large suitcase just fine. I'm considering purchasing another set for an overseas trip.
*I use the Small Cube (11" x 6.75" x 4") for toiletries. It's the perfect size for a makeup bag, brush, deodorant, toothbrush/toothpaste, and prescription. You can just take it in to the bathroom of your hotel and leave it there for the duration of your trip
*The Medium Cube (13.75 x 9.75 x 4) and Large Cube (13.75" x 12.75" x 4") are good for packing a single layer of clothes that you can just fold in half, and not have to do lots of folding. They're also deep enough to pack shoes in these two, if you need to bring lots of shoes on a trip.

*The Extra Large Cube ( 17.5" x 12.75" x 4") is good for packing two piles of folded clothes next to each other.

*If you don't need all four cubes, throw an extra one in your suitcase for things you might purchase, or for laundry. I don't use the laundry bag because a big pile of laundry takes up lots of space. It's easier to compress the clothes in one of the cubes. You could always put the cube of dirty clothes inside the laundry bag.