Hi all supermarkets open on Sundays so you shoould have no problems
regards madmum

Hi AQUAFLYTE

I take it your flying to Athens international.

I've put push pin B at Kalamaki Athens.
And Push pin A at Athens international airport.

Kalamaki Athens Marina B

Cosmos Yachting Hellas Maritime is located in Alimos nearby Kalamaki Harbour.
I looked up the Marina website and they state the supermarket is on the main street Poseidonos Avenue you can see it on the map link. They also state that provisions can be pre ordered and they provide that service.

http://www.alkyonsailing.gr/yacht_management_greece_marina_alimos.php

Bit more info here.. Mobile supermarkets operate at the Marina all hours...
I'm also finding information that the local supermarket referred to is CLOSED on Sunday's..

http://www.fyly.gr/Bases/athens.html
MARINOPOULOS opposite the marina(free delivery to yacht. )Opening Hours: Monday - Friday 09:00 am - 20:00 p.m., Saturday 09:00 am - 18:00 p.m. Sunday closed.

There are also vans from supermarkets inside the Marina, operating all hours but please note they are more expensive than the normal supermarket

http://www.yachtingpower.gr/basekalamaki.html
Provisioning: We may provide provisioning from independent supplier with van (Tasos) at our pier, operating all hours including Sunday. If you want, you may make your provisioning directly from the super market MARINOPOULOS opposite the marina (free delivery to yacht). Opening Hours: Monday - Friday 09:00-20:00, Saturday 09:00-18:00, Sunday closed.