As you will notice while walking through Lisbon, or any other town in Portugal, you will find everywhere small pasteleria's. Its the typical place where Portugese have a quick breakfast in the morning before going to the office. You will find here "uma bica", the typical strong expresso, next to a various cakes (pasteis ). The most favourite one are the pasteis de nata, Ana's favourite which you should definitely taste. The most famous location for this is in the Belem neighbourhoud next to the "Mosteiro dos Jéronimos". Over there you will find people in the waiting row to taste the Pasteis the Belem in the most famous pasteleria from Portugal. Here they actually invented these pasteis. It's worthwile to pass by if you would visit the mosteiro.
If you don't like too much sweet pastery, you can find also salty food in the pastelerias. I always take a "tosta mista" (a croque monsieur). They also serve a regular sandwich with cheese or ham. Concerning the drinks, if the expresso is too strong for you, switch to "um galão" ("lait russe") served in a glass (half milk half coffee). The best part is that having breakfast in a pasteleria remains relativily cheep. For example, you still find expresso's for less then 1 Euro. You would need to search long to find an expresso for that price in Antwerp..