Thank you for your post.
How are the users checking the items? Is this a Checkbox field? Is each line item in a related table? How are the Quantity entries handled?
Using the Send Mail script step, you can specify what information you want sent in the Message. If the Checkbox values are in one field, you can use the List ( <checkbox field> ) function to list each checked item. You can also use List ( <related field> ) to list the related records.
Does this help?
A text field formatted with check boxes will store its values in list format. Thus List (table::checkboxfield) and simply refering to table::Checkboxfield should produce identical results.
If you are new to filemaker, it can be very educational to place two copies of a text field side by side and then format one copy with checkboxes. You can then click different check boxes and see what appears in the unformatted text box next to it.