Is there a way to mimic the add item to cart so a product(subscription) is added to cart during a registration process? In short I wanted to automatically add item in the cart using Expresso Store, that is if it's possible.
It is possible to add a product to the cart by simply visiting a page so upon successful registration you could redirect them to a success page which then adds the subscription item to their cart in the background.
#productform is the ID of your form.
This can either be hidden or visible.
You could also use the Product Form Tag so that you can add multiple items to the cart with a single Add to Cart form and submit button. You would need to have something along the lines of:
<input type="hidden" value="1" name="item_qty" />