Here’s a great idea: It’s the Satechi Bluetooth Wireless Smart Keypad and it combines a number pad for your Mac with an actual old-school calculator. It even matches your Apple Wireless Keyboard.
The keypad has two modes. In one, it acts like a calculator and can be taken anywhere thanks to its built-in LCD display. In the other, it works like any other Bluetooth numberpad, sending your keypresses straight to the Mac (and presumably iOS device) concerned. It even has an advantage over a keyboard with a built-in number pad: you can put it on the left of the keypad – great for lefties or for those who don’t like to have their mouse too far away.
The price for this essential office accessory is $50.