My longest one was an uninitialized declaration of a local variable, which acquired ever-changing values.

This is why D, by default, initializes all variables. Note that the optimizer removes dead assignments, so this is runtime cost-free. D's implementation of C, ImportC, also default initializes all locals. Why let that stupid C bug continue?

Another that repeatedly bit me was adding a field, and neglecting to add initialization of it to all the constructors.

This is why D guarantees that all fields are initialized.