Call your mechanic! This is the most crucial step I will list. Ask them to give you the number of the towing provider they prefer. Why? Because the towing provider they prefer knows them, knows where they are, and PROBABLY has established an account with them. This way YOU don't have to pay the towtruck in advance.
Call the tow company. Be prepared to tell them exactly where the car is and where they can find the key to the vehicle. It is NOT necessary to stay with the car UNLESS it's blocking traffic. If your car is blocking traffic YOU WILL BE IMPOUNDED. This is not to be taken lightly as the police will come and have it impounded BEFORE the towing service you called can get there. Why? Because county towing contractors usually have too much time on their hands and have 1 or 2 drivers ready to go to your car. Contract towers MUST be available to arrive at the scene within 20 minutes. Private towers service hundreds of accounts and are much busier than county/city contract towers because their rates are lower and they don't have a fixed source of income. If you are blocking traffic or impeading safe progress of traffic in ANY way you must stay with the car to disuade officers from having your car impounded.
Ok. So your car is on a safe and quiet side street and is blocking traffic in no way, shape or form. You've called the towing company and they have given you an estimated time of arrival (ETA). Leave the key under the mat, on the tire, etc. and call your friend to pick you up.
You need not wait for the truck, they are capable of towing your car safely and really don't want to deal with you anyway. Drivers are paid on commision and can get the job done faster without you being present. They will transport your car, lock it and put your key and info in the night drop at your mechanics office as needed. Tipping is always appreciated and may encourage the wrecker operator to take extra steps to secure your car or to confirm it's safe arrival for your peace of mind.