Portable radio for cockpit communication
Buy a portable, handheld transceiver. It can very well come in handy in an emergency. Especially one with GPS, VOR, and ILS. Make sure you get a headset adapter with it.
Do not use it to save money during a long hold-short request. Turning the engine off after you have done your run up is not recommended. It is defeating the purpose of the run up. A better technique is to get your flight following discrete squawk code and/or clearance delivery electronically, by phone, or by handheld before turning on the Master and engine.