These civil demands have no bearing on your court case. Whether the store gets that money or not will not affect the outcome of your case. It is doubtful the store could even prove damages in the unlikely event they actually sued you to recover. It is best to ignore these letters. If you have prior theft convictions, they may be used to enhance your punishment on this case. Do not "go it alone", if you cannot afford an attorney, one will be appointed for you.
Save the civil demand letter. Mr. Ross is correct that paying the sum on the civil demand will not help your case whatsoever. However, you may want to discuss with your attorney paying the civil demand as a civil compromise . It prevents the prosecution if accepted by the court. This is delicate and NOT something you want to do your self.
The above is not intended as legal advice. The response does not constitute the creation of an attorney client relationship as this forum does not provide for a confidential communication.
There is no requirement to pay the civil demand letter. Restitution ordered by the court is one thing. Demands from a private law firm is another (and is essentially voluntary.)
The above is general legal and business analysis. It is not "legal advise" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
Use the money you would pay the civil demand with and put that, and then some, towards a locally experienced criminal defense attorney who can advise you accordingly given the facts of your case. Otherwise, seek the appointment of the public defender's office at your first court date so you do not have to "go at it alone," and can have an attorney by your side.