Now is a good time to buy silver if you figure your firepower situation is already good.
I cringe at current Gold prices about as much as I cringe at current ammo prices.
What I can say about the metal is stay the heck out of Numismatic stuff. One of our guys was heavily into that with early 1900s Gold Eagles, fell into some hard times and was selling them on ebay. By the time he got done with ebay and paypal fees and people screwing around with false accusations about the way they were slabbed and graded, he was worse off than if he had been just dealing straight bullion in quarter ounce increments.
Prepping gear and supplies are likely to be also readily available during a SHTF situation.
Weapons stockipiles are a dicey thing right now, and if you have weapon stockpiles, not just a nice hefty collection but an honest to goodness weapon stockpile, cache that stuff immediately. Learn how to sight in those firearms, clean them up, oil them up, seal them in proper packaging and containers and put them in the ground.
We have been losing people and assets over weapons hijack situations.
For firearms and ammo, stick to the common unless you get some real killer deals on stuff.
Lots of good quality off brand 9mm handguns out there right now coming from Turkey and some old mainstays have reasonable prices on the used gun market. The issue is a lot of stuff needing proprietary magazines, which is a real problem with the Turkish stuff. Even Ruger is screwing that up a bit with newer models not being compatible with older model magazines.
ARs, dime a dozen right now, especially if you can snag factory guns on the used market for prices which are below the cost of parts and a lower. Building ARs, from what people tell me, is not all that profitable and will not be all that profitable until the laws change for the worse, then it is risky business. On that note, the 80% lower based guns are three times the work, half the reward, nobody really wants them, but they are a good backup plan compared to guns you bought on paper.
AR magazines can't get any cheaper right now, especially when bought in bulk and staying away from the really specialized hicaps like the Surefire or Beta mags.
Optics, does not matter, they will be available if not cheaper after any ban but it seems the high end mainstays have gone nuts with pricing. Acogs going for twice the money of the rifle they bolt to.
I would not fret food, fuel or batteries as much right now, as they are still around in the early stages of a collapse except right now fuel is pretty cheap and can be worth stockpiling if you have the storage capacity for it.