I'm not aware of a reward simply for reporting food stamp fraud, but one potential route would be to file a False Claims Act case against the convenience store. There are attorneys who specialize in the False Claims Act; you could try contacting one in your area and seeing if they will take your case. Most work on a contingency basis, meaning they only get paid if they win, so it may be worth your time to make some calls. You cannot file a False Claims Act case without an attorney; it will be dismissed if you try to bring it yourself.
Call the police in Deland. It should be investigated.
R. Jason de Groot, Esq. We do not have an attorney-client relationship. I am not your lawyer. The statements I make do not constitute legal advice. Any statements made by me are based upon the limited facts you have presented, and under the premise that you will consult with a local attorney. This is not an attempt to solicit business. This disclaimer is in addition to any disclaimers that this website has made. I am only licensed in Florida.