Sacramento and San Francisco are about 75 miles apart by road. Split the difference and you arrive near San Jose, the city closest to the halfway point between them. That puts roughly 2 hr 13 min of driving on the Sacramento side and 1 hr 3 min on the San Francisco side — the fairest single meeting point among the cities near the middle.
At this range, San Jose works for a same-day meetup: close enough from both Sacramento and San Francisco to meet for lunch or an afternoon and still be home by evening.
If San Jose doesn't have what you're after, Los Angeles and Las Vegas are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Sacramento and San Francisco.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.