Anything we can think of could go wrong and probably a few things we may not think of.
I'm not going to worry to much about preparing my aquatic hobby for natural disasters and other extreme or unusal events. I have learned with a litle planning and preparation one can prevent or quickly fix a lot of problems.
I have back ups for all the important stuff, heaters, filters, filter media, replacement lamps, equipment parts, etc.
Plan to never run out of consumables that one uses routinely, including fish and plant food.
I do not use a lot of chemicals, ever. I try to avoid creating a chemical cess-pool. Most are not required.
That being said I have:
* a bottle of De-Chlor for emergency use or if I need acceptable water fast. For normal water changes, I just age the water before hand.
* a bottle of PH increaser because my tap water is a bit lower than my optimal or desired average for the livestock I keep. I rarely use it, but have it if I need it.
* a bottle of Rid-Ich.
* our laundry room always has a jug of bleach for disinfecting and cleaning.
* like wise with pure ammonia (no additives, perfumes, sufficants) for a fishless cycle.
* our pantry always has vinegar for removing calcium and lime deposits.
* likewise it always has ordinary baking soda, bicarbonate of soda.
I think a water test kit and quarintine tank is must. For the QT, most any clean, non-reactive container will work in an emergency.
Rather than planning for tsunami's, volcanos and metorites, I have a plan for power outages and home heating failures. For reasons other than my aquatic hobby, I have a generator, a small and large shop air compressor, camping cook stoves and all kinds of outdoor kitchen / cooking equipment, about 9 ways to heat water if needed. In other words I have alternative electrical power, heat and compressed air if needed.
I haven't owned an aquatic air pump since last century, circa mid-'90's. I don't need one because nothing is over-stocked. (which also averts many potential disasters)
When I had an outdoor pond, I did use the shop air compressor to keep fish alive in 5 gallon buckets. If that is the plan, consider an oil seperator and a way to regulate the airline pressure.