Other components

Floppy

A floppy disk might be useful although it is on it's way to be replaced by CD-RW. However, since they are so cheap you might as well buy one. If you are considering using an old operative system like Windows 98, a floppy may become useful for boot disks. All floppy disks are more or less the same so buy the cheapest you can find.

Keyboard and mouse

If you already have a mouse and keyboard from your old computer, there is no reason to buy new ones. If money is not an option, a wireless mouse and keyboard might be the choice for you. The advantage is that it looks better and you will never have problems with the mouse again.