A few minor updates to a custom online ordering system

Hello everyone, I've got a project that is pretty much complete, and functions well. I wrote it myself, but I'm no guru. It's all PHP/MySQL. The entire shopping cart writes everything to sessions. And on the order summary, I would like to be able to have an extra button next to each item that would add an additional product option... preferably via AJAX (for example, checking off a checkbox would add $1 to the order). I already have a little bit of AJAX implemented, but I just need a little bit more for one or two more things. It is basically just a button that adds a single extra option to any given item, and also the ability to add any additional options to each item (think text box for special order descriptions). I can show you more details upon request. And I can walk you through the order system so that you can give me additional suggestions to streamline this project. Thanks, Mike