MAKING A GOOD MINI "SURVIVAL KIT"
It took some time to find the right tin for the kit. The Romney's Kendal Mint Cake tins are the perfect size, larger than an Altoids tin (which just aren't big enough) but can still fit in your pocket: 9.5cm X 11cm X 2cm (and a bonus: cool embossed image of some badass climbing Mount Everest on the front, and if you like mint - you'll dig their "mint cakes" that come with the tin). Something to consider is that the tin itself can function as a tool: in theory, one could cook a large egg (average volume: 48 cubic cm) in a Romney's Kendal Mint Cake tin (volume: 209 cubic cm) over a campfire (NOTE: I may have to undertake this challenge someday). And the reflective inside of the tin could be used to signal a low-flying airplane, etc.
When selecting items for your own "Shit That Could Come in Handy Someday in an Emergency" Kit, keep in mind a policy of multi-functionality: why have tape when you could have tape that also glows in the dark, why have a mini LED light when you could have one that also emits UV light (to check and see if that $100 bill is a fake), and remember that things like Super Glue can also be used to glue shut an open wound. And things to probably NOT include: try lighting a fire (or just a cigarette) in a windstorm with a flint and steel, ask yourself if you really think you'll need that mini harpoon (instead of a sharpened stick), do you really need that tiny can opener, and a glowstick can be used once while a flashlight can be turned on and off. And a few of the random things I included: a Mini Multitool Hairclip (look them up; they're a light, cheap, and versatile tool) and a Handcuff Key (Yeah, not an essential. I had extra room and it seemed "a touch of badass").
Things to add: lockpick kit (not always legal or welcome in some countries; don't lose a connecting flight trying to explain why you're carrying one), sugar packet (for diabetics), electrolyte packet (for dehydration), mini bottle of Tajin seasoning (for a bland food emergency), a prepaid credit card, cash (remember, smaller denominations would be better to have in a cash-only situation; not a lot of people carry change for $100).
This is not about preparing for doomsday, this is about preparing for basic life. The need for a Sharpie or aspirin will happen.