Travel cubes are popular, but expensive. I have used drawstring bags to sort and organize clothing in a suitcase, but these work better. They make it easier to keep your packing focused/light and definitely easier to pack everything. I usually put tops in a medium sized, bottoms in large and undergarments in a couple smaller ones. Tossing in my shoes (which I put in newspaper plastic rain sleeves) on the bottom, toiletry bag (which is always packed) and then the packing cubes, I'm done really quickly. And if TSA roots through my stuff, I don't have to worry about things getting handled much. Yes, officially they could open them up and root through them, but frankly, they're probably not going to bother.
You can make them any size. Google "travel cube" or "packing organizer" and you'll get a plethora of selections. Or you can look at them at Target, etc. You can pick a size from any of them, the sizing is pretty simple to calculate, just use your own desired Height/Depth/Width measurements. Here's a couple size suggestions:
Small - finished size approx 6" x 2" x 6" (Height x Depth x Width)
Medium - finished size approx 12" x 4" x 7"
(because the zipper takes up a little length, sizes are approximate)
Small - (1) 10" x 9" (Height x Width) fabric
(1) 7" x 9" (H x W) mesh
(1) zipper at least 9" long (W) - easiest to use longer and cut off excess
Medium - (1) 19" x 12" (H x W) fabric
(1) 13" x 12" (H x W) mesh
(1) zipper at least 12" long (W) - easiest to use longer and cut off excess
(at end of posting, I have the calculations you need to select your own size)
2. Flip zipper over place short side of mesh on top,
to right side of zipper.
3. Open the zipper at least 4-5" so you can turn it right side out later!
6. The top corners are done the same as the bottom
7. Turn right side out, pushing out the corners.
If you want a different size, calculate needed fabric/mesh by knowing what finished size you want (Height x Width x Depth - H x W x D):
1) Fabric = cut a piece H + D + 1/2D + 1" by W + D + 1"
2) Mesh = cut a piece H + 1" by W + D + 1"
3) Zipper = at least W at minimum
For example: if I want a large cube 15" x 10" that is 6" deep (H=15, W=10, D=6), I would cut
fabric 24" x 17" (15 + 5 + 3 + 1 by 10 + 6 + 1)
mesh 16" x 17" (15 + 1 by 10 + 6 + 1)
zipper has to be at least 10" long.