I'm totally obsessed with how Amazon handles their database architecture, and honestly, the reason you cant find that button is because Amazon treats individual carts as isolated session objects! Its actually a bit of a nightmare from a data syncing perspective. Instead of trying to merge them—which I really wouldnt recommend even if you found a workaround—you should definitely pivot to the Shared List feature. It is such an amazing way to manage that $2k budget without losing your mind!! Heres why the list approach is way superior:

• Lists act as a persistent database that multiple users can edit simultaneously without the session timeout issues you get in a cart.
• You get better visibility on SKU changes and price fluctuations before you pull the trigger on the checkout.
• It avoids the nightmare scenario where a session cookie expires and you lose half the items your assistants spent hours finding! Just have them move their cart items to a single Austin Office list. Then you can just hit Add all to cart and you're golden. Its super efficient and way more stable for a big order like this. I love how it keeps the metadata intact across the whole team! Seriously, its the best way to handle office gear hauls... your Austin office is gonna look fantastic with all that new gear! Its a much better workflow than trying to hack the cart system tho.