How can i create an in app purchase object and later add whichever plugin i wanna buy?

I'm working on a game. I wanna know how can i continue programming the games in app purchases even without the plugin. Because i wanna know if its suitable and then buy it later. So how can i make game objects that will be in app purchases but i can use it for now to check how i can code it... Thanks... I'd like your help and if you wanna you can help me with the game. Thank you.