Hi, when you wake up you can eat Breakfast at a local Bakery (most of them are take away) at a price of 1.5-2.5 euro / piece. With 1 piece you are OK for breakfast. If you do not stay near Acropolis area you must take metro station (Red Line) and visit Acropolis and Acropolis Museum (about 3 hours + these visits). So we are almost for lunch time but before this make a 1 - 1.5 h break at Anafiotika - Plaka (about 5min walk from Acropolis) for drink Greek FRAPPE. Now it is time to eat lunch.  A cheap solution is Pita with Gyros (2.5 euro / Pita) and with 2 Pitas you do not need eat anything else.  But better prefer to eat Pita near Syntagma Square (5min walk from Acropolis) because in Acropolis are more expensive because there are tourists :(

Also some other greek foods are Mousaka, Greek Salads and as drink ouzo and raki. After lunch you can go to Monastiraki square to buy souvenirs for your friends and you find many vintages things to buy. If you have more time you can visit Ermou Pedestrian street  to buy clothes. After these walks it is time for a drink before sleep. The best are is Psyrri that has many drink bar. I propose to drink local wine. Greeks wines are famous all over the word . After this it is time to sleep :) All the areas i proposed  Acropolis - Syntagma - Ermou - Monastiraki - Psyrri are near and you can walk without need any bus. For this reason it preferable to stay near like Pagkrati - Koukaki - Kerameikos -Mets 

  PS I will write another article for 48 h in Athens for not being so hurry