For Caracas housewife Anny Valero, today is grocery day — whether she likes it or not. Here's why: It's Monday, and if Valero doesn't go now, she'll have to wait four more days to buy food.

In Venezuela, government supermarkets sell price-controlled food, making them far cheaper than private stores. But Valero explains that people are allowed in state-run supermarkets just two days per week, based on their ID card numbers. The system is designed to prevent shoppers from buying more than they need and then reselling goods on the black market at a huge markup.