updateing session variables on check box click.

Question

Hi
I need help , its very very urgent. I am making a web site related to restaurant. Where customer views course name like starter,main courses and others.
when customer clicks any of them then he gets the list of all the menu items into it.
The list get populated from date stored into the database. The customer want one checkbox on the list so that the when customer checks the checkbox it should go to the basket, and amount should get updated, same way value should decrease on unchecking the checkbox.
This is just like adding and deleting the items from a shopping cart web site.

I dnt know how to do this, using either by Session variables or another other thing. Please guide me what code i should write on "onclick" of checkbox event and update the session variable. This is very urgent for me,i need to put this live.
Thanks in million in advance.