Place the giblets, along with the neck bone in a stock pot. Add the broth, bouillon, garlic, sage, celery salt, bay leaf, and pepper. Bring to a boil.
Reduce heat and let simmer for 30 minutes. Strain the broth and discard the giblets. Return the liquid back to the pot over medium heat.
Whisk together the water and cornstarch to make a thick slurry. Add to the broth mixture and whisk to combine. Bring to a boil and cook 1 - 3 minutes until thickened. Taste and add more water as needed if the gravy becomes too thin out the gravy as needed.