If you find yourself with a dead battery, there are a few actions you can take to try to get rolling again. Jump starting and push starting are the first methods. If they both fail, try charging the battery with an AC battery charger. At least you will soon know if you need a new battery or not.
The most commonly used strategy if you have a dead battery on your hands is to jump start your car. Pull the "rescue" car up so that its front is close to the front of the "dead" car and turn it off. Connect the jumper cables to each battery--negative ends first and then the positive. Start the "rescue" car, let it run for a few minutes, and then start the "dead" car. Allow the engine of the former "dead" car to run for a few minutes to allow the alternator to recharge the battery. Disconnect the jumper cables in reverse order, being careful not to allow the ends to touch.
If jump starting doesn't work, try a push start. This only works, however, if you have a manual transmission. This is somewhat of an old technique and risky, so proceed with caution. Make sure the key is in the ignition and in the "on" position. Place the car in first gear and press the clutch to the floor. The car needs to be moving forward, so either you or someone else must get the car moving. Make sure also you are on a deserted street or parking lot. Once the car is moving, release the clutch. This forces the engine to turn over and start.
If jump starting and push starting don't work, you may need a new battery. You can find out for sure if you need a new battery by charging the old one for a few hours. Disconnect the battery cables from your car and place the battery charger cables onto the dead battery. Plug in the battery charger and allow it to run for a few hours. Remove the battery charger cables and reconnect the car's battery cables. Try to start the engine. If the engine still does not start, a new battery is required.
There are a number of items that are recommended to have on hand: jumper cables, voltmeter (this is also used to test the battery), and a battery charger. Prices can vary greatly, so shop around. If you do end up buying a new battery, be sure to keep the receipt. If you ever need to return the battery or want discounts on future batteries, having the receipt will prove helpful.
