Do you practice a "belt and suspenders" approach?

Redundant systems—belt and suspenders : a cautious approach, providing extra certainty that something will happen or that you’re ready for a situation.

(This is not the same thing as saving for a rainy day. I’m not asking about storing or stockpiling resources.)

For example, I keep a personal schedule in a local (not online) calendar on my computer, and I keep a duplicate record in an offline paper planner.

I started doing this faithfully after my computer died suddenly two years ago and left me without a schedule of appointments.

(But note, I’m not asking for help solving a schedule problem. I’ve solved my schedule problem.)

What redundant systems do you use? Do you tape envelopes shut and then staple them? Keep emergency battery-powered lanterns in case of power outages and also a supply of candles? Make two hotel reservations and then cancel one just in time to avoid a charge?