If you're on the Gaia side I recommend a stop at a restaurant and bar called Dona Maria. They also have a cigar lounge. Great views, deck, very comfortable and spacious, unlike the small, cramped restaurants that you find next to the river on the Porto side. Very reasonably priced, too. It's next to the Hilton.
We went to a port house closer to Douro, Quinta do Crasto. They offer a catered lunch, tour and tastings. It was fun but I'm not a port lover.
In Porto, the gelato shop Niva right down the street from Bolhão market is actually incredible. It looks super touristy though. There's one also in Lisbon.
I also recommend grabbing a coffee and hitting up a bakery called Ogi. Their shop is basically the back door of a Michelin restaurant. I believe they open at 9 am. I've found breakfast the least inspiring of the meals available in Portugal - at least outside of the hotels, so a great bakery was a welcome find.