Well, let's begin...

First, I created Andreyco\Cart package using Artisan.
Package and it's structure

|workbench
|-andreyco
|---cart
|-----public
|-----src
|-------Andreyco
|---------Cart
|-------config
|-------lang
|-------migrations
|-------views
|-----tests
|-----vendor

In the answers, I will use this exact package as example.

Imagine, that folder workbench/andreyco/cart/src is the application folder. If you do, you should know the most of the answers. (Actually App is package as well)

Q: how to setup routes
A: Create the file -> workbench/andreyco/cart/src/routes.php. This is done.

Q: where to put controllers and models
A: Just create controllers and models folder there.
So the TestController would be located at workbench/andreyco/cart/src/controllers/TestController.php file. Very same with models.
Directory tree would look like this

|workbench
|-andreyco
|---cart
|-----public
|-----src
|-------Andreyco
|---------Cart
|-------config
|-------controlers
|-------lang
|-------migrations
|-------models
|-------views
|-----tests
|-----vendor

I created the routes.php, TestController.php and the TestModel.php

// workbench/andreyco/cart/src/routes.php
<?php

Route::get('test', 'Andreyco\\Cart\\Controllers\\TestController@index');



// workbench/andreyco/cart/src/controllers/TestController.php
<?php namespace Andreyco\Cart\Controllers;

use Andreyco\Cart\Models\TestModel;

class TestController extends \BaseController
{
    public function index()
    {
        return TestModel::printCurrentLocation(__DIR__);
    }
}



// workbench/andreyco/cart/src/models/TestModel.php
<?php namespace Andreyco\Cart\Models;

class TestModel extends \Eloquent
{
    public static function printCurrentLocation($location)
    {
        return "Testing package controller, script is located at: {$location}";
    }
}

As you can see, I used namespaces, so you should.
Namespaces make your life a lot of easier.

Important: after creating those files, you need to update composer.json file, so that classes could be autoloaded

// composer.json
"autoload": {
    "classmap": [
        ...
        "workbench/andreyco/cart/src/controllers",
        "workbench/andreyco/cart/src/models"
    ]
},

After this, dump the changes using composer dump-autoload -o command.

Q: So, what's the approach i should follow for keeping things in the laravel way?
A: In my opinion, you should stick to packages. At least, I would. That's the way Laravel was designed to work.

I hope this helps you, good luck!

Edit
Views are not problem here. They work just like in main app package.

// workbench/cart/src/view/foldername/viewname.blade.php

<h1>Testing view file.</h1>
{{ "Blade" }} syntax is parsed as well, no problem here.

Returning view from package's controller is pretty simple

public function index()
    {
        return \View::make('cart::foldername.viewname');
    }