Can I put custom field tokens into a message template?
Yes it is possible to include custom contact fields for individuals in messages sent by CiviMail by just selecting the custom field from the list of tokens. 

The help on the Insert Token widget for CiviMail explains how to do it for custom organizational contacts, and the same process works for custom household fields as well:


  Custom tokens (based on custom data) can be added for organizations as well. These tokens will not be displayed in the list of available tokens, but can be added manually. The format is {contact.custom_12} – where 12 is the ID of the custom data field. To find the custom data field ID, go Administer > Customize Data &amp; Screens > Custom Fields and click ‘edit’ on the field you want to use. Look at the URL. The last part of the URL will be an equal sign and a number (=12). The number (12 in this example) is the id of that custom field.