Hey, there.
This is Dallas from the Social Care Team here at Shopify.
That is actually a great question. When it comes to orders there isn’t a way for you to combine more than one together. All orders have specific order numbers that relate to each of them so it would mess up some internal data and other bits of reference on the back end of your site.
With that being said, however, I may have come up with a workaround for you that would work. Once the multiple orders have been Placed by your customer you can go under Orders > Draft Orders in your Store Admin and click Create Order to make a combined order of what you are wanting.
Once you have created the duplicate orders into one you will be able to make a shipping label so that you can send all of the products out as one package rather than making multiple shipments to the same location.
Worried about inventory levels? After you have created this draft order, made shipping labels and received a tracking number you can put the tracking number into your original orders, cancel the fulfillment and delete the draft order. That way your customer will still have a reference for where their items are on their postal journey and you won’t have any inventory discrepancies.
I hope that helps to answer your question. If you would like more assistance or need more help with this let me know by replying to this forum. I am more than happy to help.
All the best,
Dallas