Athens boasts a broad selection of street food options (check the Giorgos Gyzi article). I have been toying with the idea of a contest to decide on the tastiest and best value-for-money street food option in the city. After careful consideration, I have decided that falafel wraps are the winner.
There are actually three falafel places located next to each other in Plateia Vathis (Vathis square). All three places are equally good, offering huge portions for a great price. Apart from the classic falafel wrap with the tahini sauce and the freshly-cut vegetables, try the marinated chicken skewers and eggplant filling. There are a few tables where you can sit and enjoy your wraps but most people have the food prepared to go. The National Archaeological Museum is a 10-minute walk from Vathis square so the wraps are a good local option. Bear in mind that this part of the city is a bit seedy so be cautious when walking around or being there in the nighttime.