None of those are missions.
Armored trucks are the armored trucks that spawn randomly in free mode
Collecting Bountines - Ie collecting a bounty on a players head
Completing Daily Objectives - Self explanatory
Crate Drop - random event in public free roam lobby
Destory Vehicle Targets - random event in public free roam lobby
Distract Cops - random event in public free roam lobby
Flight School - Self explanatory
Gang Attack - participate in any of the gang attacks shown on the map in free roam
Holding up a Convenience Store - Self explanatory
Import / Export Vehicle Delivery - Complete the objectives sent to you on your phone for the vehicles you can steal for money
Impromptu Race - Start an impromptu race with a fellow member of a public lobby
Killing a Mugger - Get somebody to set a mugger on you and take them out
Lester Kill Targets - random event in public free roam lobby
Losing Wanted Levels - lose your wanted levels
Plane Taken down - random event in public free roam lobby
You either do the heist, or those activities above. All of the random events will only happen in free roam. Some will appear in private ones, but others will only appear in public. But they all just appear on your phone playing free roam, you can't "trigger" them since they aren't missions.