Fixing a beef broth with too much celery seed
Bitterness is generally corrected with a combination of salt, sweetness and/or fats. 

You mention that don't have any veg at the moment -- perhaps put the stock aside or freeze until you can pick some up. Some sweet veg like parsnip and carrots could probably rescue this stock for you. Sweet herbs like basil or spices like cloves might also work, depending on what you like. 

References for flavor balancing:
 - http://www.theguardian.com/lifeandstyle/wordofmouth/2013/nov/19/balance-flavours-salt-sweet-bitter-sour-umami
 - http://lifehacker.com/learn-to-make-any-dish-you-cook-better-with-the-science-1477864259
 - http://academiewines.com/blog/2010/05/14/strategies-for-fixing-your-dish/

A herb and spice reference that might give you some ideas:
 - http://www.thekitchn.com/quick-guide-to-every-herb-and-spice-in-the-cupboard-108770