go-to

This can refer to any item or object which is the most commonly used or which you use without having to think about it, such as a food, bag, facial expression, etc. Your 'go-to x' is the 'x' that you will resort to most commonly when you don't have the inclination/time to come up with something more original, or else that you will just go to automatically. A go-to bag, for example, would be one that went with any day-to-day outfit and is suitable in pretty much any situation. If you're in a rush, you grab your go-to bag. If you're feeling unimaginative, you eat your go-to food - something quick that requires little effort but tastes good. The same principle can be applied to pretty much anything.