A live product's page in Store has a new Share button. It lists the product's address, a buy link for each option, and HTML for a buy button on another website. Each address can be copied or downloaded as a QR code (PNG or SVG).
A buy link opens the Store's Checkout page with only that item. Items already in the customer's Cart are kept, and the Cart shows them again when it is opened. An option that is sold out, or that needs a choice first (pay what you want, personalisation or a gift card), opens the product page with a note.
The buy button reads the product's current price and options from the Store each time the page opens, and links to the chosen option's buy link.