Eric-Oliver Mächler

With this Plugin you can show all your wanted Products in the Sidebar with a Widget.
Manual:
Multi-Products 
To define the right Product use the Product-Tag like [woo_products_by_tags tags=”shirt,food”]
Single-Product 
To define the right Product use the Product-Tag like [woo_products_by_tags tags=”food”]
When User click to the product in the Sidebar, they will forward to the product site.

Product Tagger

With this Plugin you can show all your wanted Products in the Sidebar with a Widget. To define the right Product use the Product-Tag like [woo_product …

Frederik Rosendahl-Kaa

Nordic Custom Made

This plugin allows you to add UpSell’s products to the cart directly from single product page. Using add to cart buttons or checkboxes. 
When using button – you can add a UpSell product directly to the cart without leaving the main product. 
When using checkboxes, the UpSells products is addded to the cart same time as the main product.

UpSell for WooCommerce

This plugin allows you to add UpSell's products to the cart directly from single product page. Using add to cart buttons or checkboxes.

Product Tagger vs UpSell for WooCommerce