If you have two orders for the same customer that you want to combine and ship together, this is easy to achieve.
Orders must have the same name and post-code for orders to successfully merge.
Both orders must also be in "New" Status
Simply navigate to the orders > overview screen - search for the customers name or post-code, select the orders and select merge orders from the order actions drop down:
The order number will now display in this format "order 1 + order 2":