I'm a big fan of precious metals, but I think you're better off focusing trying to acquire the goods you think you'll need going forward now (tools, skills, food, skills, land, seeds, guns, skills, gear, whatever, etc.) while they're easily available and then worry about silver coins for barter on the things you're forgetting.
If you were to show a silver dollar to the average person today and have them guess its' worth, you'll probably get some varied answers. Having what you need pre-SHTF will help insulate you from that awkward period when everyone knows that silver is worth something, but no one is quite sure what.