One needs plugs, spare parts and oil for that (5000 watt or higher) generator .
Rope... a throw or three of 5/8"
Tire repair kits
On and on and on...
I have a 3500W and an 1800W, both in good condition.
Something else should be mentioned, though, is that basic skills are at least as important.
Do you know how to fix a leaky pipe?
Hell, do you even know where your main water shutoff is?
Can you fix or cover a broken window if you need to?
Those sorts of things.