Can you run USB-C external hard drives on a Thunderbolt 3 port?

Hi!

Am looking at purchasing a 2017 iMac 5K (2 Thunderbolt 3 ports). Want to know if I can run bus-powered USB C external hard drives/SSDs. There are very few Thunderbolt 3 small form factor bus powered hard drives or SSDs. I understand that I will not get full Thunderbolt 3 performance but it would be nice to use USB C devices until Thunderbolt 3 ones become more prevalent.