A good quality keyboard will stand up to a lot of pounding and resist invasion by dust and dirt. A quality keyboard will generally have a firm, clean feel and the key tops will be firmly attached to their posts. Most better keyboards come with their own manufacturer's warranty. You should expect to find a small flyer or user's manual for the keyboard among the papers that come with your new machine. As with most other parts of your computer, you get what you pay for.
Mice come in both serial and bus versions.
The bus model includes its own adaptor card that goes in an expansion slot inside the computer. The serial version simply plugs into your COM1 or COM2 port. Both come with mouse driver and accessory software. Some system packages offer a cheaper mouse standard with the option to upgrade for a few dollars more. You should consider that the bare minimum, especially if you want to load a variety of software packages.