This cafeteria has been developing very slowly over the last 18 months, and I see that it has a number of favourable reviews (e.g. this from Oli Moran). It serves hot and cold drinks and snacks. It is on the road from Medinet Habu temple to Qasr el-Aguz temple, just beyond Hapy Habou and the police post on the coach park.
I visited on 4th May 2013. at 2p.m. the front door was open, but the person in charge was enjoying a sleep on the floor. It would have been rude to wake him up, so I retreated next door to HapyHabou