Gold and sliver are a great thing to have, along with all your other prepping supplies. Precious metals and food or supplies, aren't mutually exclusive of each other.
And unless you think any pending collapse will happen, literally, over night, you'd do well to invest in some metals. In 2012, some are predicting silver will jump as high as $150+ dollars an ounce. As of this post, its closer to $30 an ounce. In the coming years, some believe gold will grow exponentially. At worst, you cash it in and buy more food and supplies.
And just because the SHTF in the US, doesn't mean it will in Canada or anywhere else you may want to retreat too (Assuming you have a passport). And precious metals will allow you to obtain host country currency, despite how the USD fails.
If your really concerned about having something to barter over the long term in a SHTF scenario, then your at least counting on some sort of society and structure to stay intact in your local. community. In which case, your better off learning a primitive living skill or some other skill you can barter with. Gardening, passive solar, hunting and prepping, ammo reloading, trapping, first aid, herbal medicines, etc etc. Or something that will allow you to grow your trade power. Chickens continually provide eggs. Some people can make soaps from scratch.
Regardless of what you do, you can't really go wrong with having some precious metals as part of your survival plan. After you have water, food, heat and shelter sufficiently covered.