RE: Adding storage space to a Laptop
Really the best option is to buy a bigger laptop, and make sure you purchase one with the proper size and specs that would allow a secondary hard drive to be inserted. As mentioned also, you can also forgo having a CD Drive, in order to have a secondary, if the laptop isn't big enough to fit two HDD's and a CD drive. And after all, they also have attachable CD drives via USD, if you still want to use one.
I do know that if you go to a site that you can customize the order, you can tinker what is available to expand with, based on the size of the laptop, and it's capabilities. Also check with how much it costs. Generally with the cheaper ones, you would need to remove something to make space for other hardware.