You never know when you may need to "live off the land". Whether you are in combat, or are forced to leave  whatever situation you are in, having a few basic items can make a great deal of difference in your survival.

I carry this kit in my right BDU pocket or in my pants/coat pocket when I'm about town. The idea is to ALWAYS HAVE IT ON YOU. You may have to dump your ruck or may have to shed your web gear.
The items below are very basic and can be changed to fit your needs.

Knife - Small folding lockback. or multitool. In addition to this, I carry an air force survival knife on my BDU Belt. Glue the sharpening stone to the back of the sheath and you can carry more stuff in the stone pocket like a Gerber tool. Forget the Rambo knives, they're useless junk.

Matches - Strike anywhere, cut in half.20 matches is quite a lot for survival since this is just a small kit. Fires might be eliminated anyways depending on the situation. Add fishing supplies around it. 4lb line can be used for sewing and lashing too.

Lighter - Small lighter wrapped in reynolds wrap to keep clean and dry. Lighters have a hard time lighting in extreme cold.

Vaseline/cotton ball fire starters - See article on how to make these wonders

Water tablets - A better idea would be a couple Chlor-flok pills which would take up less room.

Candle - Can be used for light, heating or to start fires. Will last longer than matches and stay lit better. Animal fat candles can be eaten for food. Use harder wax over soft wax since they can melt in the container. Hence all the reynolds wrap.

Garbage bag - 100 uses. Poncho, camouflage, carry bag, solar still, tree still, water bag etc. Next time I'll cover it with paper then wrap a layer of 100MPH tape around it to protect it.

Twist ties - Use them with the condoms to tie the tops off

Compass - Small watchband type removed from plastic housing. Can be swallowed if needed.

Condoms - Main use is to carry water. Put into sock and can hold a liter of water. Add tablets and tie off. Wrap package with 100MPH tape to protect and for God's sake use un-lubricated!

Bouillon cubes - Can be added to water in condom for a little bit of a morale boost. Also food tabs could be carried. An M258A-1 container will hold 3 days worth.

M258A-1 container. Warp the container with some 100MPH tape and then 550 cord. The lid has a striker from a match box glued to it. Very strong and can be used to hold more water. Use real 550 cord which has 7 inner strands which can be used for lashing or fishing. Melt the ends to keep from fraying

Other items to add:

small bandages - they can be notched to be used as butterfly sutures too

safety pins

Needle and more fishing line - Sewing your arm like Rambo will probably do more harm than good, but you can sew your pants. Fishing line can be used instead of thread.

A slightly larger pill container can hold some fire starters, matches and fishing supplies and take up less room.

If you carry a sidearm, wear it on your BDU belt instead of your web belt. That way if you ditch you webgear you are still armed. Berretta with 4 spare mags = 61 shots! Much better than nothing!!!