no matter what your local laws are, and how you respect them or not, please have at least a rear (red) reflector: while you will immediately notice your front light failing, you probably won’t notice that your rear light is dead before a long time;
bring backups: old, cheap, light lights will do; in case one of your main lights fails, you can always get back home or to a safe place with your backup, even if you have to go significantly slower with those weaker lights;
a powerful headlight can serve as front light backup, and it is jolly handy when you have to fix something on your bike (change a punctured inner tube for example), which can turn into a nightmare otherwise, considering you only have 2 hands (or when you start dropping stuff in the grass…).
A few personal advices about that: