graceful degradation: how to handle service outages

We've all had that moment, right? A crucial service we depend on just goes dark. So, what are your best tricks for making your systems handle that kind of failure without completely falling apart? Are you using circuit breakers, setting up fallbacks, or have you got some other clever idea? I'd love to hear about what actually works in the real world and what you've learned the hard way after an outage.