aptis: i.e. accommodated to the circumstances of their bearers, as definitely explained by inanis; the idea is carried out by the addition of expeditis, here in the meaning of ‘light,’ but suggesting, from its commoner use, the idea of soldiers in light marching order.
 tabulis: account-books.
 expensum: the word expected, if there was actually aliquid lucelli, is acceptum (cf. Pl. Most. 297 “ratio accepti atque expensi” ; Cic. Rosc. Com. 1.4 “in codice accepti et expensi” ), but Catullus means to indicate his presumption that all accumulation was that of debt.
 pete nobiles amicos: ironically spoken in self-apostrophe: the suppressed conclusion is something like sic irrumatus fueris. Neither the Pisones nor the Memmii were new families; the former claimed descent from Numa ( Hor. AP 292 “vos [Pisones] o Pompilius sanguis” ), and the latter from Mnestheus, the comrade of Aeneas ( Verg. A. 5.117 “Mnestheus, genus a quo nomine Memmi” ).
 nobis: i.e. Piso and Memmius.