Breakdowns. Fires. Flat tires. You name it, it might happen. Most people have had an accident without proper equipment to even make minor repairs.

Do not end up like this.

[edit] Steps

Get a plastic toolbox or other container. It should be just big enough to keep your items.
Get items:
- Small first aid kit. Everybody gets injuries on the road. Keep it stocked and replace used items.
- Torch (Flashlight) and spare batteries. Preferably with a orange or red 'blinker' light to warn traffic.
- Food. Items like cereal bars, power bars, etc.
- Water. Keep jugs or bottles of water in the trunk. Water is important for cleaning anything or to prevent dehydration.
- Notepad, pen, or pencil. Post-it notes are handy.
- Whistle. Preferably with compass and thermometer on it too. Keep a fish and chip fork inside the mouthpiece as it has a variety of uses; other than just eating!
- Electrical tape. To make minor repairs.
- Cigarette lighter. You never know when you need fire.
- Cleansing wipes. For when your hands, arms, or any other part of you gets dirty working on the car.
- Tissues. Have a variety of uses.
- Plastic rain poncho. In case of rain.

Also helpful: Used In emergency to signal to rescuers.

- Safety pins. Useful to repair clothing or as a fishing hook.
- Playing cards. Something to do to pass time while waiting for assistance.
- Magnifying glass. For looking at small parts of the car and starting small fires if you don't have a lighter.
- Matches. Waterproof matches are best.
- Cotton wool. Useful to clean wounds or as timber for a fire.
- Curry powder/assorted spices. For emergency food flavoring. Ever eaten a rat?
- Tin foil. Variety of uses.
- Compass. In case you get lost.
- Triangular bandage
- Multi-tool. This should include assorted screwdriver heads.
- Local maps. In case you get lost or need give some one directions on your location.
Keep in the glove box:
- Small fire extinguisher. In case of fire, of course.
- First aid kit. Injuries are possible anywhere and you might not be able to get to the other first aid kit in the trunk of the car.
- Gloves. For work and warming purposes.
Keep in the boot (trunk):
- Jumper cables. In case you need to start your engine using another car or to start another cars engine.
- High-visibility vest or similar. It is important to be able to be seen by traffic and rescuers.
- Spare tire. In case you get a flat tire. It is also important to make sure you have the necessary tools to change said tire.
- Warning Triangle. In Great Britain, these are mandatory in the case of an accident. Remember! Your hazard lights are only a secondary source of warning. Place 45 meters from car on both sides if possible.