When it comes to monetizing your game, there are plenty of options out there. However, if you wish to implement them successfully, that will depend on both the nature of your game and your own creativity for making them really work on your behalf. Knowing how to sell a product will help you a lot. That means you should go beyond the idea of making money simply by showing ads. There are many more opportunities you should be aware of. For instance, here's a very good guide you could use for thinking about monetization in terms of sales strategies and not merely as a drag-&-drop service to subscribed to.
As you start exploring various sources of revenue and wrap your mind around the idea that thinking as a salesperson is an important skill to have, how about making and selling physical products using your game as a theme? Making and selling swag featuring your game somehow could be an interesting possibility to entertain. I'm talking about selling mugs with funny messages only your goofy main character would say, or a t-shirt displaying your game logo that you could sell or promote in a giveaway campaign aimed at bringing exposure to your game.
Of course, you should, first of all, make sure that making and selling products based on your game is a good idea. Would your players really buy that? Why? What kind of products specifically? The good thing is that you don't need to worry that much about all the logistics involved in making, selling and shipping a product. Well, at least that's the case for some services for which I provide some brief descriptions below.
The Monetizr will create a full-fledged swag shop for you, where your customers will find all they need for purchasing any of your items directly from your website or your social media; as well as from Unity, iOS, and Android games. Once you submit a logo, they will put your game-art on caps, t-shirts, hoodies, stickers, phone cases etc. You don't need to stock, create, ship, handle returns, or manage any merchandise nor to maintain, secure, or arrange payment processes. They will ship worldwide, and if the buyer is in the US, it's free shipping for all orders! Cool, right? You can check it out here.
Spreadshirt doesn't have the same resources found in Monetizr for bringing your merchandise to your customers straight from your game, but it will also allow you to create a storefront for selling your amazing stuff with your game them. Don't be fooled by their name. They will make more than just t-shirts. Check them out here.
Ponoko will turn a 3D model into a physical product. How about turning your game character into an action figure? Explore their website to learn more.
Like in Ponoko, you can use Shapeways to upload your 3D model and make it into products. They will also give you a storefront. Click here and see if it's for you.
Here's another interesting idea: you could sell the original soundtrack of your game through CDBaby! Find out more about that here.