Is there a way to daisy chain USB3 external hard drives?

In theory you should if the drives have pass-through USB ports. I don't know every drive enclosure there is, but in my travels I've yet to see one. However, if you have a pretty good USB hub or powered hub that supplies enough power, then you can connect more than one USB drive to the hub. The trick is finding a good USB hub. Preferably Thunderbolt powered. 🙂

If you want to spend some money look for a Thunderbolt Dock such as the one sold by OWC. It comes with two Thunderbolt ports (one used to connect to the computer) and five USB ports, an Ethernet port, and more. I bought one and quite like it. I believe I've seen something similar on Amazon.com, but do not remember if it was cheaper or more expensive.

That's a USB 2.0 hub. If the computer has USB 3.0 ports you might look for a 3.0 hub. You can tell by the blocker in the port. White is 2.0 while blue is 3.0. Of course this isn't relevant unless speed is critical. USB 2.0 is fine for background backup such as Time Machine.

Sounds like me when we travel. I have one for the same thing either to use on my 2011 MBP 13" or, lately, on my new 2015 MacBook. They are so useful for those odds and ends. 😀

I use an iMac and added one of Mobee's port expander that mounts in the cable hole in the rear on the stand. Very nifty. Around here I have lots of USB 3.0 drives because Thunderbolt is too expensive.