So with pretty much every laptop coming with a SSD these days (or you are upgrading to one) the lack of large of amounts of storage is pretty apparent. The good news is most modern laptops have usb 3.0 ports which gives you the full throughput that portable 2.5" external hard drives can deliver. The biggest issue if you use your laptop on well your lap is it's pretty inconvenient to have this hard drive tethered to your laptop which doesn't easily move around with you.
So I started looking into different ways to attach the hard drive to the back of the lid of the laptop. I've tried suction cup hooks like you can find in craft stores. There are some Christmas wreath hangers that kind of work but are rather large and the hook is the wrong shape. The idea is to suction cup the hook to the hard drive and then hook it over the top of the laptop screen. Plastic hooks are obviously preferred to prevent scratching. Also, it has to be small enough not to obscure the screen. Then if the angle/curve of the hook isn't right the hard drive won't hang right. Also, it's pretty easy to knock the hook off the laptop or the suction cup could release. Overall, it was a pretty horrible solution.
Next I tried those thin rubbery sticky pads used to hold cell phones to car dashes. Those kind of work but were hard to remove and as the stickiness wore off the hard drive would fall off. This was an even worse solution with strong possibility of damaging your hard drive from a fall.
Finally, I found a solid solution I REALLY like. Those little rubber coated flexible spider mounts are perfect for the job. They are really inexpensive like these for $2.55. Those ship from china so it takes a few weeks. Search around amazon and you can find some prime ones for a bit more. Look at my photos to see how you should bend them to wrap around the hard drive and create 2 hooks on the opposite end of the usb port. When bending sharper angles like for the hooks you might want to use some pliers. Just be careful with these cheaper mounts because you can actually have the metal underneath poke through the rubber outer coating. The rubber coating makes it safe to use and grips so it doesn't slide around. You can bend all the little legs to fit almost any hard drive and any laptop. Now, when you get up or move around with your laptop your external hard drive moves with you. For hard drives I really like the Seagate Backup Plus slim 2TB for around $89.