There is a light meal on the EZE-GRU segment and lunch after departing GRU (or the other way round?), and breakfast just before arriving at LHR. Club Kitchen is available at all times.

Since the flight is in east direction, shortly after departing GRU it starts to get dark, cabin lights are turned off, and I think the best option is to sleep, if you can.

If you can read spanish (or at least you want to see the photos), I can refer you to a couple of trip reports I wrote about this route.