Even if they are non negotiable, it is good to know what their value is. Company websites often provide some details. Also, you can ask.One thing that complicates the issue is that if salaries are themselves opaque, then benefits are even harder to find real metrics on. Sure, sites like glassdoor and salary.com can help compare, but at best you only get a range of salaries at a company/career field to look at and nothing/next to nothing on benefits. So it can be really hard to tell if the benefits a company is offering are good as compared to other companies in your field.
And from what I've been told, most benefits packages are non-negotiable for new grads like myself anyways.
What is your policy on PTO?
What percent of the health insurance premium is paid by the company?
How long until I am vested in the 401K match?