You can add an online store to any STANDOUT template by embedding the HTML code of the store through Add Element > HTML, as simple as that.
Below is a list of some popular stores:
1. PayPal buttons: the simplest e-commerce solution – https://www.paypal.com/pdn-item
2. Google Store Widget: embed your own store and get paid using Google Checkout. More details can be found here: https://www.ecwid.com/google-sites
3. Embeddable 3rd party store: there are currently multiple online services offering free embeddable storefronts like WePay, BigCartel, Shopify and more.