A small tin can carry vital equipment for emergency use in a survival situation.  I spent £22 with Amazon to get Limitless Equipment's "Survival Kit Mark 1", although you could put one together yourself.

The one I bought contains these 10 items:

1. An emergency whistle and fire-striker - the whistle works easily and the fire-striker creates sparks which can ignite a small piece of cotton wool or cotton from a tampon (also included);
2. A rough wire which acts as a saw - it has a handle at each end and is useful for cutting wood;
3. A compass that can be critical in avoiding moving in the right direction - especially it it is dark or cloudy.  Also it's more reliable than using the sun for directional guidance.  There is also a pencil and paper supplied, which could be helpful for maps and record-keeping;
4. A fishing line with a hook, float and weight.  Very useful for catching fish for survival;
5. A small torch.  At first I thought it wasn't working then realised it had one of those seals you have to peel off before the battery connection can be made;
6. A plaster or wound dressing useful in the event of injury, along with a sewing kit, safety pins, cleaning swab and a sterile blade;
7. A coffee filter for helping to purify drinking water, along with water purification tablets and rubber bands;
8. A condom, useful for carrying water from a stream to a campsite or base;
9. Various bits of metal - a copper wire, and paper clips.  Also various ties for fixing things and a long string;
10. The tin containing all the survival items - which is itself useful for cooking and conveniently includes sachets of sugar and salt.  A sheet of silver foil is also included.