With only 8 days, keeping to no more than two cities makes sense. Since you love food and wine, I would recommend splitting time between Lisbon and Porto. If you are going in warmer weather, you might consider splitting time between Lisbon and the Algarve (for the beaches).
Lisbon
It is a bustling city with plenty to see and do, including day trips to Sintra and Evora. In October last year, we stayed in Lisbon for 5 nights and frankly, we could have stayed there longer. Lisbon is also surprisingly relaxing. They have the most amazing viewpoints (miradouros). We stayed in an aparthotel in Chiado and had one about a 5 minute walk with a lovely bar/coffee place, rose garden, and majestic views. When it wasn't raining spent a lot of time their just relaxing. These miradouros are all over the city, so find one close to your hotel and enjoy amazing views.
As for restaurants, Lisbon has so many choices depending upon your tastes and budget. Our favorite is Oficio in the Chiado. It is a local Portuguese tapas restaurant with really inventive food at a reasonable price. You will see lots of young professionals and families at the restaurant. I still remember the tomato salad with a basil granita and the oxtail rice dish. A great selection of Portuguese wines. We went back there twice on our trip the food was so good.
Also, would highly recommend a dinner with a Fado performance. There are two places that we enjoyed. One is a bit more casual, a small place with an artistic bent on classic Portuguese food, in fact, the restaurant, Tasquinha Canto do Fado is in Mouraria, hosts some of the most inventive street art. The Fado performances typically start between 7:30 and 8:00 p.m. depending upon season.
The other Fado recommendation is O Secredo in the Alfama. This is a much more upscale experience with outstanding food, the cod is their speciality, but if they have the pork cheeks on the menu, you must try that. This Fado performance may feature men as well as women.
Finally, taking a food tour is. a great way to learn more about the city. Eating Europe and Devour both have excellent tours.
Porto
This is a great place to visit, especially if you like Port and good food. There is a great variety of restaurants. Our favorite was a low-key restaurant featuring beef sandwiches and amazing value on wines and a very Special Sangria. Of all the restaurants we ate in Porto (including some high-end ones), this is the one that my husband still talks about as his favorite.
I would also recommend that you take a day tour to the Douro Valley. We did and it was amazing to visit two small wineries, have lunch, and explore the country side. While the tour included port tastings, one of the wineries we visited had Sparkling Wine (which was surprisingly good).
I would also recommend that you take a food tour, we did the one by Eating Europe and were able to visit one of the few Portuguese owned Port houses. The cellar tour including bottles of wines over a hundred years old.