Minimalist and high-efficiency plugin under 1,000 lines of code packed with WooCommerce up-sell features: Frequently Bought Together, Out-of-stock Alternatives.
Feature: Frequently Bought Together and Product Recommendations
Generates recommended product relationships from purchase history by email address using the Action Scheduler.
Creates a short code and dynamically inserts a frequently bought together promotion offering customers a percentage discount on add-on products.
Uses real dynamically generated WooCommerce Coupons to aide with reporting and other compatibilities, thus coupons must be enabled in WooCommerce settings.
Feature: My Account Order Again Discount (beta)
Adds a button to the My Account Orders page to reorder for a 5% discount.
Feature: Out-of-stock Alternatives
Displays two up-sell products above the add-to-cart form on single product pages when out of stock. Converts traffic to otherwise dead end discontinued or temporarily unavailable product pages.
Screenshots

Frequently Bought Together feature on a single product page.

Frequently Bought Together dynamic coupon in the cart.

Out-of-stock up-sells displaying on a single product page.