Living in a very active earthquake zone i have a bag i keep stocked up in case we need to make a quick exit.
The contents change depending on the season, not much need for a sleeping bag here in summer so i replace that with more water.
I also have 2 tents, a winter one and a summer one made of reflective material to keep it a little cooler.
Off the top of my head roughly this is what i keep year round:
Pretty comprehensive home level First aid kit with 2 weeks supply of prescription medicine (regularly rotated).
Water filters (2 in case 1 fails) and purification tablets
Box of 6 x 1.5 Litre bottled water
Food, exactly what changes as with the prescription medicine it's regularly rotated (should also say i also include food for the dog)
Washing stuff, soaps, shampoos, toilet paper, hand wipes etc
Shelter (as above different tent depending on summer or winter)
Sleeping mats
Sleeping bags and/or wool blankets
Clothing (again depends on the seasons)
Couple of flashlights with spare batteries and car charger
Camping stove, cutlery, pots and pans
Sun block (stays in as i regularly get sunburnt ever in winter)
Duct tape
Paracord
Tie-wraps
Few basic tools like wire clippers, adjustable spanner, knife, shovel etc
Tarp (extends camping area)
Mosquito spray/treatment
Radio
Spare batteries for phones etc with car chargers.
Copy of all important documents
Sounds like a lot of stuff, but it's basically my backpacking kit with bells on.
Should also say that the plan is to stay near one of a few places i know of with out of the way natural wells.
I wouldn't drink straight from them but that's why i include water filters and treatment tablets.
I figure with that lot we should be ok for 3 days.
If we're out the house for longer than 3 days then it's probably fallen down or burnt to a shell, if that's the case then certainly before 3 days was up, we would have moved to one of our other houses or will be staying with family/friends.
If it's still standing then the chances are we would have needed the bag to get out while the after shocks hit.
We're on the top of a hill so flooding is not a worry, so it's really only in the case of a fire or earthquake i envisage needing it.
Hopefully it's a waste of time and never gets used.