Part of the game is to go around tagging supplies for the rebels to retrieve later.
The next logical action would be for the rebels actually go retrieve the tagged supplies.
So, once all story missions for a particular province are complete, add rebel supply/medical/fuel convoy side-missions to that province.
You accept a mission and provide security support to the rebel convoy travelling from point A to point B and help fend off any attacks. If the convoy arrives safely, then you get some extra XP.