Small padded case that I can throw into a suitcase and keep my laptop protected, then pull out and tuck under my arm or in a carry on and don’t have to worry about laptop getting dinged
Another essential - great padding and I love that the inside is lined with corduroy. This is extra great b/c it allows you to use any bag to carry your laptop. The timbuk2 products are super durable too.
I have this is black to carry around my iBook. I'd surely buy a new one to fitthe MacBook air that I win if I needed a different size. It does a great job protecting, whether in a tote bag or on it's own. I shopped around for a while and this was the best I found by far.