My.02:

The cell network is going to get overloaded shortly after the first incident. The network is only designed fo 10 15 percent peak load. SMS and long distance land lines are going to be the most reliable means of communication. Maybe VOIP plus WiFi.

Select cell towers have battery backups. IIRC, Verizon is the best and AT&T is the worse. You will have between 2 and 8 hours if cell service after lights out.

Forget getting anywhere via car in an evacuation. The roads are going to be jammed untill well out into suburbia. A good plot point would be a pair of walking shoes for commuting, and dress shoes kept at the office. Less likely, but still feasible, are a nearby bike shop and a wad of cash, or membership in a sailing club.

There should be more then one rendezvous point. Places where one party can wait for the other one. Have character A check,the backup locations before circling back to the prearranged one and camping out in their truck.