I use the smallest one for work - my laptop cord, my ten-key, my travel mouse, and my jump drive fit nicely in the bag.  The medium and large one are great for smaller clothing items and health/beauty items in my carry-on.  Make sure you look at the dimensions on these - I wasn't paying attention and thought they were larger then they are - but they ended up being useful anyway.  (I purchased larger ones for my clothing after receiving these.)

The smallest one gets the most use - and it is still holding up very well after four months of constant use.