The plastic bag is an unlikely symbol of economic frailty. But in Indonesia, the soaring cost of that humble everyday item is raising uncomfortable questions about the country’s future growth prospects. At a market in Depok, south of Jakarta, the plastic bags Budi needs to sell his chicken have nearly doubled in price. “Plastic is really expensive right now,” he said in an interview on April 17. “Usually, I’d have to set aside at least 10,000 rupiah (58 US cents) for plastic bags, but now, I...