Transporting your laptop safely without a bag?

Tomorrow I have to take my (quite expensive) laptop on the train (and bus for short) with me, but I don't have a laptop bag. What is the safest way to transport it? Would you rather pack it in your suitcase or backpack?

If the laptop was quite expensive, I wouldn't skimp in the wrong place and just go buy a laptop bag. They are not expensive.

Neither a backpack nor a suitcase protects your laptop or can secure it. You could also use a plastic bag.

Suitcase. A backpack is too soft.

So I always pack my laptop in a sturdy plastic bag (very important to protect against crumbs and possibly rain!) And put it in the back of my backpack. I've been doing this for years, nothing ever happened. You just have to remember, of course, that there's a laptop in there when you take off your backpack and put it down! And you are not allowed to give the backpack out of your hand either.

In the suitcase. Well padded by the clothes.