OK, my bad - I figured this out, finally. Wrong section of snippet to highlight. That part works. Here is the real answer:
Use this Liquid doc page to reference order variables: https://shopify.dev/docs/themes/liquid/reference/objects/order
If you add this code to the packing slip the final prices will show up:
order.subtotal_price {{ order.subtotal_price | money }}
order.tax_price {{ order.tax_price | money }}
order.shipping_price {{ order.shipping_price | money }}
order.total_price {{ order.total_price | money }}
In my code, with the original snippet inserted, that is at line 147, just after the {% endfor %}
I have no idea why my example packing slip had the total price. Mystery.
Formatting and labeling is left to the reader.