If you buy gold buy silver too! Unless you are buying an insane about of weight, then buy coins. There is no tax on currency so it costs less. Go to a coin shop and tell me you don't care what you buy but that you want the most weight for your money. They might have stuff there or it might take a few days for them to track stuff down. Be sure to compare the prices to online prices too.

Some coins are cheaper than others. When the price goes to the moon I doubt the more expensive ones will still be worth that much more. So getting as much weight as possible is probably the best idea.