You could always download the game onto a portable flashdrive. You can get one pretty cheap. Plug it into an internet-accessible computer, have it download on the flashdrive (it'll probably be called something like F:/ or G:/) instead of the harddrive (which is usually called C:/), safely unplug the flashdrive, and then plug the flashdrive onto your home computer.
You can transfer the files from the flashdrive onto your computer, or keep all the files handy onto the flashdrive so you can carry them around with you. Just make sure to keep an updated copy of the files on your computer if you do, in case you lose the flashdrive.