Hi Guys,
You are most likely looking for the line_item_properties which is where these extra bits of information get stored on the order. An order can have many line items (products), and each line item can have many properties.
I'm no expert on the variables in Order Printer, but you are most likely looking for something like:
{% for prop in line_item.line_item_properties %}
{{prop.name}}: {{prop.value}}
{% endfor %}
I'd place that within the {% for line_item in line_items %} loop that is in the documents.
This will then loop through any properties on your line item and output the name of the property (for example: "Color") and then the value (for example: "Blue")
Sorry to plug our app here but OrderlyPrintv2 can do this, in fact line item properties are already built in and will automatically be included in your documents ;)
Hope this helps!
Bjorn