You need to have outstanding print material to hand out to interested trade show visitors. What you give them should depend on their level of interest.
At the very least you should give interested trade show visitors a business card, so they can contact you later. One sided cards can be good if you need to make notes, things like show specials and quotes. These are low cost and can be displayed prominently at your trade show booth.
Postcards and leaflets offer space for a bit more information and are excellent for advertising trade show specials. These should be colourful, well branded and contain powerful copy. As a general rule, less is more. Statements should be short and to the point.
These may be picked up from your trade show booth or handed out. It's up to you.
A brochure is a great way to communicate a lot of information for a small price. We recommend having information-rich brochures on hand to give to more qualified visitors to your trade show booth.
Leaving these around your trade show booth is not a good idea, as they may end up in the bin.