Over the last 10 years I have observed that the folks that do NOT own precious metals are the ones that always say it won't do you any good in SHTF scenarios. The banksters have done their job on these folks, very well. The folks that DO own precious metals are the ones that try to decide how much and which types. They know the banksters have lied to them, and are not going to get caught flat-footed when the financial world goes crazy.
I have been an advocate of owning precious metals, because history shows that is what ultimately passes for real money on this rock.
This advice is about as close as one can get to the functionality of precious metals in your SHTF preparations. Except that gold is especially good if you plan to survive the immediate scenario and thrive in the future, after the chaos has subsided:
Being the chronological age I am now, my priorities have shifted since I first dealt with this issue. We already WENT THROUGH a SHTF scenario, in 2007, and I did very well with gold.
We are likely to go through an even worse SHTF scenario within the next year or two. Gold will be good to have as the dollar continues it's collapse that started just recently.
Traditionally, late July and early August are the best times to BUY gold. Early December is the best time to sell gold, IF you are a speculator. If you are buying gold to hold for it's store of value, then buy NOW, and don't worry about the "paper price" of worthless dollars. Hold onto it like it is priceless, until you absolutely HAVE to part with it.
As always, DIVERSIFICATION is the best option. Some gold, some silver, some lead, and some steel, are ALL wise to have. Of course, you need to balance these with food, durable goods, and MOST importantly, CLEAN WATER.
Specifically answering your question, buy an equal number of ounces of both gold and silver bullion. If you can get NON-governmental bars or rounds (no official government coins), you get the most metal for your money. You pay LESS premium for bullion than you do for official coins, AND you get PURE metal, instead of alloyed for circulation. Also, you want to buy One Ounce denominations. The premium you pay for 1/2, 1/4, and 1/10 ounce coins is very stiff. I would only buy partial ounces if I was exclusively buying gold. Silver value is small enough that you would not have to divide a one ounce round. You would just accept more "product" or some other items as "change" for the balance of the round, OR just write it off. If you are concerned about having smaller denominations, because you intend to be actively trading/bartering, then spend $500 for a bag of "junk silver" (U.S. silver coins of pre 1965 denomination). Half dollars, quarters, and dimes minted in the U.S. before 1965 are 90% silver.
The reason I said buy equal number of ounces is because you will be using silver for transactions that require "money" to purchase items that can't be bartered for. Gold would only be used for very LARGE purchases, i.e. a vehicle, land, livestock, etc. That, and silver "prices" tend to fluctuate wildly, while gold prices are fairly stable. Gold is usually 75 times as expensive as silver (currently), so if you had equal number of ounces of each, when the SHTF, the value of silver will go up faster than the gold (because, historically, the gold silver ratio is 16:1), and you will make faster value gains on the silver as the G/S ratio declines from it's current 75:1 ratio down to it's 16:1 ratio, which is going to give you more purchasing power in daily use. Folks will not be able to "make change" for gold rounds, unless they have lots of silver, or smaller than one ounce denominations, and are willing to forego the premium.