When you are exhibiting at a conference there are lots of prospects and partners who will pass through, and some will make more sense for your business than others.
There are some people who stop at a booth strictly to grab whatever is being given away. Those people are the reason to have a low-end parting gift for these non-prospects.
After determining that there is not a good likelihood for a business relationship with a visitor to your booth, have a pen or something around that range to send them off with.
And when you have people stop by who are current partners or prospects that seem to have a lot of promise, keep some nicer items aside for them.
These quality giveaways reinforce my loyalty in their brands and display to me that they value our relationship.