There's a newer accessory pair you might consider adding to your existing computer or ordering on your next new one. This certainly doesn't fall into the "necessity" category, but I have used mine for several months now, and find them very handy as compared to the traditional wired devices. I'm referring to the combination packages of wireless keyboards and mice.
What I've found -
There are several manufacturers offering these now. Logitech and Microsoft each have several models, and there are others. The prices seem to be running from about $30 up to about $100 and the stores are putting them on sale with rebates too. As far as I can tell, the differences on the keyboards are mostly in the "extra" keys which are included. The mice are all at least the 3-button variety and are all "optical" designs. The optical mouse is, in itself, a desirable upgrade as it has done away with the roller ball mechanism and replaced it with a red light. All ball-type mice will eventually have mechanical problems. The optical mice aren't subject to that. Some of the wireless mice have additional buttons, as are found in today's wired mice. I will leave that choice to you as my personal preference is to limit my own mouse to 2-buttons and the center roller.
The keyboards have all the usual keys, but most come with a number of extra keys. These extra keys are programmed to do such things as control the volume of your sounds (and music), open your mail program (Outlook, for example), call your favorite search engine (such as Google), open your Instant Messenger program, etc. Some have the mouse features built into the keyboard in the form of a trackball, as a secondary way to move the pointer around. That particular feature is aimed at the folks who like to lean their chairs back, put their feet up and work the keyboard from their lap. (I hear authors like this idea.) With the mouse functions right in the keyboard, they can do it all from the keyboard alone.
How they work -
With wired equipment, you have a cord for the mouse and another cord for the keyboard. Well, with these packages, you have a small "sender" unit, smaller than a pack of cigarettes. The single cord from that sender forks into two connectors. One plugs in where your old keyboard did, the other where the mouse was. There is no separate power cord. The mouse and keyboard require two batteries each of the standard AA size. Some units have a cradle for the mouse which recharges the AA batteries while you are not using the computer. Your choice again. The keyboard seems to use up the batteries very slowly (over many months) but the mouse I have eats up a pair just about once a month.
You install the software/hardware, install the batteries, it all starts to work. The sender unit seems to have a pretty good range on my Logitech model. I seem to be able to sit back 6 or more feet and it communicates just fine. When the computer boots up, the pieces reconnect automatically.
Oh, these work just fine when added to a laptop as your home-office full size keyboard and mouse!
Why do I like them -
You will be surprised to find how nice it is to not have the cords to contend with. This is especially true of the mouse. You will never have to tug on the cord again. Theoretically, these do not save space on your desktop. However, it will seem like they do. The freedom to move them anywhere, if for nothing else than to dust the desktop more easily, is very nice. Some gadgets just turn out to be good!