At this point I don't think they have much in the way of drones or vehicles yet. Once they knew defeat was coming as the SDF and SAA advanced into their territory, they'll have stockpiled weapons and ammo in caches. As for feeding themselves, same deal, stored supplies, no different than how the Taliban operates/ed from caves and hideouts. At this point IS is down to hardliners and has few urban areas left so I'm not sure if they're paying salaries anymore. Anything else they need would come from raids, conscription, and looting. Their propaganda arm seems to have mostly been offloaded to foreign and online activists and you can track their decline in the decreasing quality of their combat videos.