Time Out Market, spend as long as you can there - it's utterly fantastic. It's a food hall but nothing like the St Enoch centre one!
Red Frog - a really good speakeasy style cocktail bar. Must make a reservation but it's worth it.
A Cevicheria - Great ceviche bar with a cool Octopus hanging over your head. It was near my airbnb but worth the trip. I went for lunch and it was brilliant. There's a lot of ceviche in Lisbon and it's generally all good.
Mini Bar - It's a restaurant, it's good fun and the food is brilliant (foie gras ferrero rocher mmmmmmm).
I stayed in the Barrio Alto area, quiet during the day but at night it's great. Loads of little bars (many just a hole in the wall and you just drink on the street), lots of friendly people in good spirits. You just grab a beer and walk around, then grab another one, it's great.
Take good shoes, it's very hilly. It's very cheap though!
I've just reread your post and see you're going with friends. Time Out, Red Frog (if they are cocktail fans) and Barrio Alto in the evening for sure!