If you can only get one, get the Kaos trap. It'll be hard to come by later.
And if you can get more than one, include the Kaos trap. No matter what, get the Kaos trap first.
Just like what everyone else is saying. I recommend getting the Kaos trap on day one. Supplies are limited. But if you don't get the trap, as far as we know you're going to have to get it through the dark edition. I'm getting the trap on day one.