Two-player co-op and Steam Remote Play
Quick answer
Deadly Days: Roadtrip supports two-player couch co-op and remote play through Steam Remote Play. The invited friend does not need to own or install the game; make sure one player has a controller.
On this page
Prepare the session
Start with the host's installed copy of the game and a connected controller. Open the Steam friends interface and send a Remote Play invitation to your friend. This is a streamed shared session, so confirm that the invitation is accepted and that the controller is recognized before trying to start the run.
Check who controls each survivor
If the second player cannot join, first check the connected controller and the Remote Play session. Do not buy a second copy merely to solve an unclaimed local player slot. The developer's official guide specifically describes inviting a friend who has not installed the game.
Plan both backpacks
Version 1.0 adds cross-backpack synergies: selectors can mark equipment in the other player's bag. Check the highlighted target cells after either player reorganizes. A change that improves your own layout may remove a connection your partner depended on.