What?
I probably won't forget this but just in case I do, this is an article to explain how I got the shipping address from a sales order in Zoho Books into the template of the Package Slips.

Why?
It took me a while of playing about with the placeholder reference fields in the template before Zoho advised on a 'hidden' away setting which was key to changing what these display.

What I had: 
${CONTACT.CONTACT_DISPLAYNAME}
${CONTACT.CONTACT_ADDRESS}
${CONTACT.CONTACT_CITY}
${CONTACT.CONTACT_CODE} ${CONTACT.CONTACT_STATE}
${CONTACT.CONTACT_COUNTRY}
and in my Sales Order: 
BILLING ADDRESS          SHIPPING ADDRESS
-------------------      -------------------
Test Company             Joels PO Box
1 Test Street            1 Different Street
Test City                Another City
Test State Test Zip      Another State Another PostCode
Test Country             A different Country
But the packing slip would display the Ship to address as the same as the billing address... Or more specifically, the primary contact, company, address and phone from the customer record and not from the sales order change.

How?
The key is a setting you need to change by going to Settings > Preferences > Packing Slip Settings > and Enable "Delivery To":
Zoho Books - Settings Preferences Packing Slip Settings Delivery To

Then change the Shipping Address Format either under "Customers and Vendors" (although this applies to all templates) or under the specific template.

I wanted to do this for just the Package/Packing Slip, so:
  1. Go to Settings > Templates > Package Slips
  2. Edit the template you want to change this on
  3. In the left button menu, click on Header
  4. Scroll down and click on Shipping Address Format (Custom)
  5. Enter the following placeholders: 
    ${CONTACT.CONTACT_ATTENTION}
${CONTACT.CONTACT_ADDRESS}
${CONTACT.CONTACT_CITY}
${CONTACT.CONTACT_CODE} ${CONTACT.CONTACT_STATE}
${CONTACT.CONTACT_COUNTRY}
${CONTACT.CONTACT_ADDRESS_PHONE}
  6. Done

Source(s):