// Note: Doesn't work when falling off a bike (-> wiki)
// 
// Somewhere before OnPlayerExitVehicle & outside functions / callbacks
new
    last_vehicle [ MAX_PLAYERS ]
    ;
    
// Add / edit the callback
public OnPlayerExitVehicle(playerid, vehicleid)
{
    last_vehicle [ playerid ] = vehicleid;
    return 1;
}

// The function.
stock GetLastPlayerVehicle( playerID ) 
{
    return last_vehicle [ playerid ];
}