We already have a community exchange system, it is called CASH!
From what I gather from going to a few meetings about currency issues, 97% of all money in circulation is "funny money" that is created by the banks as interest bearing debt. The remaining three percent is cash issued by the government through the Reserve Bank of New Zealand, which unlike the U.S. Federal Reserve Bank is 100% government owned. That's not to say that the RBNZ is a benign institution, as it is still a part of the overall system of usury that is the root of all our problems, but at least our(!) government owns it.
It draws a wry smile from me when I see people I know are involved in TTNZ paying for shopping with eftpos. I wish these people would realise that every time they do this, or write a cheque, take a loan or use the bank in any other way they are "feeding the monster that enslaves them".
Endeavour to transact as much as you can in cash. If you must keep a bank account, keep it with a state supported bank such as Kiwibank. Keep only enough money in it to do the things that you absolutely cannot do with cash. Forget the convenience aspect of it - this is war, and some inconvenience is to be expected.
For me, I guess, this is easier, as we are market sellers of home-grown organic produce, and our customers pay cash. If, however I was doing a job where I had to be paid into a bank account I would withdraw the bulk of it as cash and spend it as cash. Don’t worry too much about security, just hide it well and don’t carry more on your person than you need. Better to be robbed than taken as a slave!
Convert all your spare money as soon as you can into tangible assets such as land, infrastructure and tools. Obviously you need to keep a bit by for emergencies.
Never take credit from a bank! This is the modern equivalent of selling yourself into slavery. Better to go hungry and buy all your clothes in the op-shop.
If the demand for cash is greater then the amount in circulation, it will be increased by the Reserve Bank to ensure that the demand is met. No government can be in a position where people go into the bank to get cash and there is none. More cash transactions mean the banks are starved of their life-blood. If the banking system goes into freefall people will still need to buy and sell stuff and those who have real cash money will be able to transact when the eftpos card is just a piece of worthless junk.
Complementary currencies are just for fun. The IRD won’t allow you to transact your main revenue generating occupation in them and the only thing you seem to be able to get for them is massages and bicycle mechanics. I need to pay the rates and put fuel in the truck and pay my agricultural contractor. Cash will do all these things and the bank can butt-out of my business. Cash is utilised in face-to-face transactions, thus it automatically stimulates the local economy, but is still "legal tender for all debts public and private" where complementary currencies are not.
I would encourage you to keep proper account of your transactions and pay your taxes just as you would have to if running your business through a bank account- squeaky clean keeps you out of jail (mostly).