They earn money (or barter for basic goods like flour, cheese, wool etc.) by mending pots for villagers and similar work.

The rest of their diet consists of cheese, small fruits and nuts and wild root veggies, edible wild greens etc. They can't grow them (they are nomads!), they gather them in woods and so on on their way. They are probably dependent on external supplies most of all in winter.

They're not agriculturalists (yet, a great many of their Aiel cousins are), but it doesn't matter anyway. Seed Singing was not agriculture as such but an aid to agriculture, making the farmers' crops impervious to diseases and more productive. The farmers grow and reap the crops, Da'shain/Ogier/Nym wandered the countryside to Sing to their fields each spring.