I found a tip of a knife or razor in my food, can I sue the restaurant

Thank goodness no one was injured. In a negligence or strict product liability suit there needs to be provable damages for a matter to 1) be worthwhile, 2) get past a motion to dismiss and 3) go to a jury for deliberation. Thankfully because no one was injured, litigation is not the recommended approach. You got a free sandwich and have put the police on alert so the store will clean up its act.

Well done.

Good luck.

NOTE: This answer is made available by the lawyer for educational purposes only. By using or participating in this site you understand that there is no attorney client privilege between you and the attorney responding. This site should not be used as a substitute for competent legal advice from a licensed professional attorney that practices in the subject practice discipline and with whom you have an atttorney client relationship along with all the privileges that relationship provides. The law changes frequently and varies from jurisdiction to jurisdiction. The information and materials provided are general in nature, and may not apply to a specific factual or legal circumstance described in the question.