Calabrian chili paste brings a unique fruity heat and umami to dishes that standard red pepper flakes just can’t match. If a recipe calls for it and you’re out, your best substitute is a mix of Harissa (for the pepper fruitiness) and a dash of red pepper flakes for the sharp heat. Sambal Oelek also works in a pinch if you need pure chili flavor without the vinegar tang of sriracha.