Use a standard assignment statement to create a new session variable, as follows:
<cflock timeout=20 scope="Session" type="Exclusive">
<cfset Session.ShoppingCartItems = 0>
</cflock>
Use the structdelete tag to delete a session variable; for example:
<cflock timeout=20 scope="Session" type="Exclusive">
<cfset StructDelete(Session, "ShoppingCartItems")>
</cflock>