I respectfully disagree that circulated Australian 5, 10 & 20c coins are worthwhile stacking in the hope 'maybe when prices go up'. By this I mean not in any large quantity, keeping your loose change for a rainy day, to show your grand kids or a numismatic perspective is a different proposition. I'm talking strictly about the metal content in current Australian coins only here.
There is no silver in modern Australian coins.
Copper, nickel and bronze (an alloy of copper) are used as money but that's not their major use. Electronics, bearings, plumbing, batteries, marine applications and stainless steel are common.
I make my living from metal and I have processed thousands and thousands of tonnes of it.
Non precious metals, even the more valuable non ferrous stuff, (copper and related alloys like 5/10/20c coins, bronze (mostly Cu & Sn), brass (Cu & Zn), and nickel allys like stainless steel) are not worth saving in commercial quantities for any length of time. No business does this, unless they have made a mistake and over paid for it in the first place or are in a jam. The simple logistics of storing non precious metals and security concerns make it unfeasible.
You need to process shipping container loads of the stuff to just make a living, let alone a tidy profit.
Where will you store it? Real estate is valuable and can be better utilised. How will you secure it? You cannot leave coins, brass or copper out in the open like steel, (druggies will steal it). You would need a whopping great safe to store even just ten tonnes. You could hold the equivalent value of gold in one hand. Easily.
Getting off topic here, but a full shipping container load of steel is only worth about two ounces of gold at the moment.
If I wanted to make money I would invest into real estate/machinery or something that gives a return. If I wanted to 'stack' it I would go with gold or silver.