Ryan on "logging every cookie/session issue in an sql table"

In the session_tokens meta_value I am seing a long hex string (as the top key).

If you parse the cookie of a logged in user:

wp_parse_auth_cookie('', 'logged_in');

You'll get something like this:

Array
(
    [username] => (username)
    [expiration] => (timestamp)
    [token] => (randomstring1)
    [hmac] => (randomstring2)
    [scheme] => logged_in
)

The token randomstring1 is run through a hash function (either sha256 or sha1) and that's the value you're seeing in the database.

Is it related to the wordpress_logged_in_****** stuff in the cookie?

The part after wordpress_logged_in is actually the site URL hashed:

md5(get_site_option('siteurl'));