For (γαρ). Explanation of the reason for asking her.

Were gone away (απεληλυθεισαν). Past perfect of απερχομα, to go off. They had already gone before she came. To Sychar (John 4:5; John 4:39).

To buy food (ινα τροφας αγορασωσιν). Hινα in purpose clause with first aorist active subjunctive of αγοραζω, old verb from αγορα (marketplace). See Matthew 21:12. Τροφη (nourishment) is old word from τρεφω, to nourish (Matthew 3:4). "Victuals" (plural).