Here's a nice, common App Service Provider I created and use in 100% of my applications. It provides a simple way to define and bind contracts, define model observers as well as extend form validation extension.

AppServiceProvider.php

<?php

namespace App\Providers;

use Illuminate\Support\ServiceProvider;
use Validator;

class AppServiceProvider extends ServiceProvider
{
    /**
     * List of contracts that will need to be bound to their implementation.
     *
     * @var array
     */
    protected $contracts_to_bind = [

        // Repositories
        // 'Repositories\\UserRepository',
    ];

    /**
     * List of models that will need to be observed.
     *
     * @var array
     */
    protected $models_to_observe = [
        // 'User'
    ];

    /**
     * List if custom validator extensions to register.
     *
     * @var array
     */
    protected $custom_validator_extensions_to_register = [
        // 'validation_name' => 'SomeClass@method'
    ];

    /**
     * Bootstrap any application services.
     *
     * @return void
     */
    public function boot()
    {
        $this->bindContractsToImplementations();

        $this->observeModels();

        $this->registerCustomValidatorExtensions();
    }

    /**
     * Register any application services.
     *
     * @return void
     */
    public function register()
    {
        //
    }

    /**
     * Bind contracts to their implementation.
     *
     * @return void
     */
    public function bindContractsToImplementations()
    {
        foreach( $this->contracts_to_bind as $bindable )
        {
            $contract        = "\\App\\Contracts\\{$bindable}";
            $implementation  = "\\App\\{$bindable}";

            app()->bind( $contract , $implementation );
        }
    }

    /**
     * Assign observer to model.
     *
     * @return void
     */
    public function observeModels()
    {
        foreach( $this->models_to_observe as $model )
        {
            $eloquentModel = "\\App\\{$model}";
            $oberverClass  = "\\App\\Observers\\{$model}Observer";

            $eloquentModel::observe( $oberverClass );
        }
    }

    /**
     * Register a custom validator extensions.
     *
     * @return void
     */
    public function registerCustomValidatorExtensions()
    {
        foreach( $this->custom_validator_extensions_to_register as $name => $action )
        {
            Validator::extend( $name , $action );
        }
    }
}