Special instructions at checkout

We want to add a place for customers to enter special instructions at time of checkout. (either asking us to install a clasp to a watch band, special shipping instructions, etc.) I cannot find a way to do that. Is it possible?

Thanks, mimib

I should add -- we want just one place to enter text on the shopping cart page. It was suggested to us once to add a text box as an item option -- but that shows up everywhere an item shows up and then is not editable at check out time. We want a single text box for special instructions at check-out time which is not tied to any single item in their cart.