You may be offered a snack on the short haul flight in First (banana, chocolate bar, potato chips).
>> Wondering what is the best product: ex-Conti or ex-United? <<
Soft product wise (service and food) they're the same, and imo better than the pre-merger United.
As for hard product, the seats are the same pitch, though I find the ex-UA seats a little more comfortable. There is no in seat video on ex-UA short haul, only the CO 738/9 that have DirecTV installed. The (ex-UA) A319/320s are also having the overhead screen IFE removed completely and having wifi installed. The wifi will be charged for but there will be a free streamed domestic IFE offering. It's a bit of a mess trying to work all this out as United is doing so much to their domestic fleet right now.
>> And can non-Gold *A access lounges on domestic flights? <<
Generally No. United domestic First does not automatically get you access to a United Club. The only possibility you have is if you are connecting off a Business Class international flight on the same ticket/itinerary. But I don't know for sure.