Some of the most common reasons for roadside assistance are:
Out of gas:
Unless you are traveling long distances in a remote area, carrying cans of gasoline in your trunk is not advised.
Pull well off the side of the road to a flat surface.
Make sure the vehicle remains in gear.
Be sure the spare has air before you start.
The spare on most vehicles is designed only to get you to someone who can fix or replace the damaged tire!
As soon as you are back on the road, head for a service center.
Check your owner's manual before attempting to jump-start a battery.
Once the battery is charged - this will take five to ten minutes - head for the nearest service center and have the root cause fixed!
Jumper cables will help you rejuvenate a dead battery, but remember batteries don't go dead by themselves. Look for obvious causes - broken fan belt or lights left on.
For less than $5 you can buy a magnetic key holder that affixes to the underside of the vehicle, usually in a wheel well, and it holds a spare key for your doors and ignition. But his only works if you do it before you need it!
Stay prepared for a safe trip!