I think they might have bought bread judging from Epicurus's famous "gloating" about living on less than a penny.
I addressed the quote from Seneca about the "penny" in a post from January:
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Diogenes Laertius 10.7:
he spent a whole mina daily on his table, as he himself says in his letter to Leontion and in that to the philosophers at Mitylene.
[ U158 ]
Seneca, Letters to Lucilius, 18.9: The great hedonist teacher Epicurus used to observe certain periods during which he would be niggardly in satisfying his hunger, with the object of seeing to what extent, if at all, one thereby fell short of attaining full and complete pleasure, and whether it was worth going to much trouble to make…
he spent a whole mina daily on his table, as he himself says in his letter to Leontion and in that to the philosophers at Mitylene.
[ U158 ]
Seneca, Letters to Lucilius, 18.9: The great hedonist teacher Epicurus used to observe certain periods during which he would be niggardly in satisfying his hunger, with the object of seeing to what extent, if at all, one thereby fell short of attaining full and complete pleasure, and whether it was worth going to much trouble to make…
Don
And, yes, the Garden (ho kēpos ο κήπος ) would have included vegetables and fruit. If you search around on the site here (or take a look at my paper on the location of the Garden in the Files section) you'll see some description of the size and use. They would not have exclusively lived off the land, however; no more than any other ancient Greek living in the city of Athens.