Many years ago, I developed a pocket survival kit to serve my needs.  While there are many similar kits out there, I found them to be lacking in key areas.  I was able to create the kit when I found the metal box I use.  It was manufactured by a company called Olicamp.  It is stainless steel with a rubber gasket locking lid, and measures about 4"x6"x1.5".

The focus of the kit is getting me through an unexpected stay in the outdoors.  The scenario I imagine would involve if I lost all my other gear or got disoriented while just walking off into the woods for a moment.  I want to make sure that I get through the night, so the kit is built around getting shelter and fire as quickly and easily as possible.  After that, I ensure I can have potable water, and then worry about gathering food.

I carry the kit in a simple cloth bag I sewed myself.  Its purpose is to cushion the box while it's in the cargo pocket of my BDU pants, and to act as part of the water carrier (more on that below).  I have carried it many times in my cargo pocket, and I hardly notice its there.

Here is a photo of the items I carry in the kit.

 

The Box - Made of heavy gauge stainless steel, it is rugged and large enough to use as a cooking pot or drinking cup.  The clips that hold on the lid can be used to attach a handle, to make a more practical pot.
The Lid - The lid has a rubber gasket around it so it protects the contents of the kit from moisture.  The inside of the lid is polished, so it can be used as a signal mirror.
Water Purification Tablets - This is an unopened bottle of iodine based water purification tablets.  The 50 tablets are enough to purify at least 25 quarts of heavily polluted water.
Plastic Bag - This bag, placed inside the cloth bag the kit is carried in, can be used as a water carrier.  Also important because the purification tablets need some time to work.
Waterproof Matches - I carry about 25 water proof matches.  This the easiest way to start a fire.
Tape - The tape is to repair any holes in the plastic bag, or for general purposes.
Button Compass - This is just one of those tiny compasses that are often found on the wrist watch bands.  It is, of course, limited in its capabilities.  It will only provide a rough indication of my true direction.  But for this size kit, it should be adequate.
Magnesium/Flint Bar - This is the same thing as the larger magnesium and flint fire starters but in a smaller version.  It is about half the size of the GI style that you find in most stores.  I picked this up at a gun show years ago, and its perfect for this size kit.
Whistle - The whistle is an important way to summon rescuers.  It saves your voice, is louder, and more discernible.
Plastic Magnifier Lens - This is one of those small fresnel plastic lenses that are sold in drug stores for helping people read fine print.  The large area can focus the sun and can quickly start a fire.
Fishing/Snare kit - In this ziplock bag, I have an assortment of hooks, line, sinkers, and snare wire.  I also have some safety pins, needle and thread.
Space Blanket - I consider the space blanket one of the most important parts of the kit. Waterproof, and heat reflective, it is the fastest way to get under shelter if caught out in the elements.
Wire Saw - A wire saw is a fast way to cut through branches for building fires or shelters.  It is the SAS style saw, made of multiple strands of wire braided together.  The rings that came with it were left off to save space.
Hacksaw blade part - This came with the magnesium fire starter, and makes a good striker for the flint.
Razor Blade - This is a long razor blade used for surgical prep.  It could be used for minor surgery, or as a general cutting tool.

Some of the things that could be added to the kit

Flashlight - A mag lite solitaire would fit well inside the kit.  I carry one on my key chain, so I left it out of my kit.
Candle - I used to carry a tea light candle in there, but in the summer heat in my car, it melted.
Bullion Cubes - Some bullion cubes would be a good addition.  They don't provide much nutrition, but they can provide a warm drink, or flavor natural foods.

What about a knife?  Well, I carry a lockblade Swiss Army Knife at all times, so this would be in another pocket anyway, so why bother carrying an inferior blade inside the kit.

First aid gear?  Well, in a kit this size, it would be difficult to carry any significant amount of medical gear.  I do have a separate first aid kit that I carry.

Bulldog