I've been on our mtb clinic committee several years. We did the t-shirt thing a few years, but one year had bandanas printed with our design. A multi-use item, some people use them as a sweatband. Me and my allergy-pone nose used to struggle with tissues all the time until someone told me to carry a bandana. Clean ones are good in some first aid situations.

Other things I've gotten and liked are the gels and energy bars.