I have founf the following goes down well
USB sticks
Clothing (tshirts/caps etc) but only if they are of a good quality and not simply something with a massive logo
Good quality playing cards
Mints (always useful for the meetings)
I think a good quality binder with note paper etc in would go down well especially as you would use this after the event in meetings
pens are always useful (currently sitting here with my Star Partners pen in my Vegaspartner/GoldenStarNetwork pen pot 
)
Brightshare’s yo yos went down well once
Overall it can’t be super big or heavy as people need to take them home in their luggage, it also needs to be something they will want to use after the event. My girldfriend is in insurence and gave away realy good quality branded golf balls – May not work in our sector but they went down a storm with her clients