Branded promotional bags are a useful advertising tool and should still be viewed as relevant in the digital age. As such, its use should be considered by all industries.
Promotional bags are generally used long after the event at which they are acquired, generating ongoing publicity for the organisation displayed on the bag. This prolonged use and subsequent brand awareness, can effectively pay for the initial cost of the bag to the business. Consumers enjoy getting something for free, which leads to positive connotations with the company giving away the product. Additional positive links with the organisation will come from the perceived environmental concern of producing a reusable, practical item.
Expos are an ideal occasion to use the power of promotional bags. Regardless of the contents, the outside of a promotional bag will be the only part on display and will attract people looking for a free gift at such events.
[Source]
http://www.innovate2006.co.uk/how-promotional-bags-can-benefit-your-brand/