Is there a way I could display a token (for exmaple user ID) as a default field content to a content type?
Do you want it to be editable or not?

Either way, its going to take a small custom module with hook_form_alter or hook_form_FORM_ID_alter if you want to target a specific form.

If you want it editable:

http://api.drupal.org/api/drupal/developer!topics!forms_api_reference.html/7#default_value

If you want it set at a value:

http://api.drupal.org/api/drupal/developer!topics!forms_api_reference.html/7#value

Start with downloading and enabling devel and a small module with just this to get a list of all the form elements on a page:

function YOUR_MODULE_NAME_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  dsm($form_id);  // print form ID to messages
  dsm($form);  // pretty print array using Krumo to messages
}