Don't gamble your safety by messing around with cheap plugs. When you hear that "click click click" of a nail in your otherwise perfectly good tire - get your tires patched. If they are old get them replaced. The Metairie Road Shop across from the library works till four but everytime I showed up they helped me out and got my tire patched and me underway in about 20 minutes for under 25 bucks.
Pros: Helpful and Knowledgable Staff.
Cons: You may have to wait if you don't have an appointment - they can get busy at times. They don't stay open late.