This is one of those things you didn't know you needed until you use it once and it changes your life. Traveling with packing cubes is an organizer's dream and will make sure that your clothes and other essentials don't get mixed during the packing and unpacking process. And best of all, packing cubes actually help you maximize space in your luggage (unless you have a spherical suitcase...then nobody can help you).
Seriously, they are the best. And at this low, low price on Amazon, you can't go wrong.
If you don't know where to start, here are some recommendations: