I believe this conversation could go two directions depending on your financial status. If you have significant wealth, there are many opportunities to diversify your portfolio with precious metals. If you would like more information, feel free to PM me. (I am not a broker, just have some knowledge and experience.)
However, if you are just getting by month-to-month like many of us, here are my thoughts.
First, precious metals do not just have value because they are shiny. They were also used in many ways for many years. Their practical usage led to their inherent value. While they lost many of their uses during the industrial age, the computer age has provided many new uses for them. Therefore, no matter what happens, they will keep some type of intrinsic value.
That being said, I invest in copper, nickel, silver, and lead. I have simple, cost-effective methods for each which I will detail below. I believe each of these offer a simplicity in obtaining them as well as usability in a SHTF scenario. There is one drawback to this type of investing, it has a size and weight liability. A hundred dollar bill takes up a lot less space than 10,000 pennies.
As mentioned above, if anyone would like to discuss any part of this topic further, I am available for PMs, phone calls, and/or in-person discussions.
** I left out gold because I am not able to afford it. However, what I say about silver would also apply to gold.
Silver - The increased practical use of silver has led to its increase in value over the last decade. It is currently out-performing gold. Because of its usability, availability, and flexibility, it is a great investment opportunity. If you are looking to out-perform the S&P 500, you shouldn't be here. However, if you want a practical way of holding actual wealth, it is a great option. *Coins and jewelry are practical ways to collect this metal.
Nickel/Copper - Both of these metals are used in many ways. However, they are also readily available right now, so their value has not increased a lot. It could even be argued that they are not "precious" metals. However, as they are necessary and because they are readily available without risk, I collect them. *Coins seem to be the most practical way for me to collect these metals.
Lead - Not considered a precious metal and is readily available. However, as mentioned earlier, the usability in lead in the form of bullets makes it quite valuable. Should the SHTF scenario include a collapse of our financial system, I do agree that bullets will be a recognizable "currency" with which one would be able to barter. The beauty of this option is you can shoot your collection. Bullets of any caliber and really any composite would be a worthwhile investment.
* Coins: To start, if you are using coins as a method to collect metals, you need to have a basic understanding of the two components that comprise the value of a coin: numismatic and intrinsic. Simply put, the intrinsic value of a coin is what the metal would be worth if you were to melt it down (melt value). The numismatic value is what additional worth has been added to the metal because it is in the shape/size of a coin and the quality of that shape. So, because a coin has a known quantity and purity of the metal, it is worth more. (No scales needed.) To many, because of the beauty and/or rarity of a coin, it is worth even more. Should the SHTF scenario redefine our quality of life, numismatic value would most likely decrease. Let these factors guide you when you decide what type of coins you will purchase.
Silver - I only invest in "junk" silver coins. These coins have been so worn that they hold little to no collector value. However, because they are a certain size/weight, they offer a usability far beyond bars and jewelry. I avoid collectible coins because once either type has been melted, they are worth the same. You need to keep abreast of silver's value. If you shop carefully, you can find coins in many locations. Since their is a value to silver beyond their coin value, there is a risk of losing value in them.
Nickel - Our nickels are still made of nickel. While nickel is readily available now, it could become more scarce in the future. Here is the real beauty of keeping nickels. They are still worth five cents. So, you can't lose anything in their value. 20 nickels can be had for a dollar and can buy a dollar's worth of goods/services. Therefore, it is a no-risk investment against currency. (It is obviously still susceptible to inflation, but all currency is.) So, whenever I get nickels in change, they go into the nickel jar. Not a grand investment scheme, but still a hedge against future possibilities. (A story to illustrate a point. When I was younger I collected bicentennial quarters. Several years ago I found a bank full of them. Upon careful research I learned that each one of those special quarters was still worth 25 cents. So, I took them all to the bank and traded them in for nickels. Only the numismatic value of the quarters could go up, but the nickel value of the nickels could go up. Since they are both worth the value printed on them at the time, it was a no-risk, equal swap.)
Copper - Copper is similar to nickels except that it is not as available in coin form anymore. In 1983, pennies switched from primarily copper to primarily zinc. Therefore, collecting copper is a little more risky. (At one time, copper got to a value where a copper penny was worth 4 cents. Now that its value has declined, anyone buying copper pennies for 4 cents has lost value.) The good news is that copper is low right now so the risk is low. You can get wheat pennies for 1.5 cents. So, you could obtain them and still keep 2/3 of their currency value. I don't actively look to purchase copper coins, however, I do check my change every day and have a jar for any pennies made in 1982 or earlier.
If you have read this far, I apologize for being so long winded. I am actually cutting it short as this discussion warrants much more information. However, I will once again offer my availability to anyone who would like to discuss these ideas further. Possibly once our new home is more established, we could start a category pertaining to this topic.