What are the laws of eating before Maariv?
May one eat non-mezonos/ non-hamotzi even after nightfall, even if he doesn’t have a shomer or a set minyan?
Yes, non mezonos and non hamotzi foods have no restrictions before Maariv. Up to a Kbeitzah of mezonos/bread may be eaten.
Shulchan Aruch O:C 235:2, Mishna Brura ibid. s”k 16