I'm convinced, when the SHTF, junk silver will be the thing to have in your possession.
1) Even gold bullion coins of one form or another, people will remain skeptical of since they won't be familiar with the source. Hence, assay costs and the time needed to do so, will make gold use initially impractical, even for large purchases. Similarly for gold jewelry to be used in trade - any smart person will insist on an assay.
2) Gold will have such a high unit value when the SHTF, it will be impractical to use for small(er) everyday purchases. Larger purchases and international or interbank settlement of accounts, excellent choice.
3) Meanwhile most people are familiar with the form and precious metal content of late-era (pre-65) coins minted by the US govt, back before Nixon closed the gold window. These are coins that can, generally speaking, be trusted, and will find common use since an assay and/or verification of authenticity wouldn't seem to be needed.
4) Silver will have a low enough unit value (certainly, lower than gold) such that these coins will be very useful for everyday small transactions. Like, Ron Paul's dime for a gallon of gasoline. How fitting!!! That's why personally, I'm not opposed to a bi-metallic currency standard. I just think the market will work these things out.