It's standard practice for an employer to ask a departing employee to sign a severance agreement. Such an agreement typically contains a clause promising not to sue the employer, and giving up all legal rights the employee might have against the employer.
While severance agreements are reasonable for employers, they might not necessarily be in an employee's best interests. It's not a bad idea to retain a lawyer at an hourly rate to review the release, and to flag areas of concern. And while you're at it, why not ask for better terms?
Every situation is different, and this isn't one-size-fits-all list, but additional terms that could include:
+mutuality of releases. Employer and employee release each other from all claims.
+mutuality of confidentiality. If the employer wants confidentiality, make it mutual. Employer and employee agree not to discuss (a) the severance agreement; or (b) the employee's employment; or (c) both.
+mutuality of non-disparagement. If the employer wants an agreement that the departing employee won't disparage the company, make that mutual. A large company can't instruct everyone who works there, but most employers are willing to identify a few people who will be instructed not to disparage a departing employee. This mutual non-disparagement clause can be useful if you're leaving a company where there were shared bad feelings.
+an agreement not to contest an unemployment claim. An employer can't guarantee that a claim will be accepted by EDD, but most employers are willing to agree in writing that they won't dispute a truthful claim for benefits.
+a letter of recommendation from someone respected in the company.
+removal of negative information from a personnel file.
+if characterizing the end of the employment relationship is important, some employers will agree to allow an employee to resign rather than be terminated. This face-saving gesture can be useful later on when interviewing for a new position and the question comes up about "Why did you leave your last job?"
+Additional severance monies.
+Additional months of health insurance coverage.
Good luck! You can handle this!