Always have enough cash on hand to purchase a tank of fuel and some groceries. It isn't uncommon for the systems to go down for a few hours or a day. It doesn't happen often, but it does happen. When it does, plastic cards have no value.
In Whitehorse one day, it was cash only because the system was down. Stores could take cash only and banks were also off-line.
One trip down the Alaska Highway, Toad River lodge could take cash only. We needed to stop for the night anyway so did that, but the system still wasn't functional the next morning so we paid cash for our fuel and carried on.
Our telecommunications infrastructure isn't the most reliable.