I've implemented WooCommerce on a food take-away site, where all the items are on a single page.
Adding to cart is slow - about 4 seconds. The server is fast. We've tested on various sites and servers, and WooCommerce's add-to-cart (via AJAX) is always slow. Normally it doesn't matter, because somebody is not wanting to add lots of products in quick succession. But on a take-away, they are.
I've written many WooCommerce plugins, and don't mind diving into the code. But I'd be grateful if one of the plugin authors could give me a clue about where to look. Any ideas where the bottle-necks are? Any low-hanging fruit?