In Latin, the word for some is not-none. nullos amicos habeo. I have no friends. nonnullos amicos habeo. I have some friends.
But a different expression is used with Nouns that tend to be used only in the Singular. Say, money, food or water. Then the appropriate expression is I have something of money. I have something of food. I have something of water. aliquid pecuniae/cibi/aquae habeo (where pecuniae, cibi and aquae are all in the Genitive Case).
On this page Marcellus is speaking of specific money – the money quam argentariae debeo which I owe to the bank. That is the reason why he says he has something EIUS pecuniae of THAT money. The eius anticipates quam argentariae debeo.
‘I have something of that money which I owe to the bank,’ Marcellus says. He puts his right hand into his pocket to pull out the envelope.