This menu is unlocked after completing the main story quest Mario's Rebel Drops. This very helpful feature allows you to request for weapons and vehicle drops from your allies, almost anywhere in the map. You can only request for weapons and vehicles you have unlocked. Complete more challenges, find more collectibles, and liberate more settlements to unlock more options to your rebel drops.
Each drop requires a rebel drop beacon. You can only carry one but you can resupply from any liberated outposts. While exploring, you may experience "encounters" where random NPCs may ask for your help like towing their car, delivering a vehicle, or opening a gate. Some rebel NPCs will also ask for your help in more risky encounters such as rescuing a captured rebel vehicle, hijacking limo and pose as a driver to assassinate the passenger, and many more. These encounters will unlock additional beacon resupply points when completed successfully.