Oh, and once I got a custom Ember Mug, which was very nice.
Also, Im not sure if this is a client gift or you're activating at a booth, but the MOST popular booth activation I did last year was "Aura Photography"
We hired an Aura photographer to come to our booth and take photos, then they put them on a branded card, but people LOVED it. Also very unique and unusual for a conference.
https://www.innerlightaura.com/events