Seeing as your looking for stuff you wouldnt "normally" find in headshops.. id say your trying to be ahead of the curve, a little innovative? thats what i love to hear!

my instincts point towards..

A. any kind of obscure hemp products to sort of show off the versatility of the plant:
hemp clothing and other textiles, sandals and shoes, tote bags and hats, etc. also hemp oil products such as hand lotions and whatever other beauty products for the ladies you can find..

B. any smoking/glass/grow/culture related reading materials, and more:
you could put furniture in your store a few couches, chairs and tables. people can look at your reading material available for purchase. we all know the typical ones like hightimes and skunk but you can also get glass aficionado stocked, other glass journals and grow journals. you can get DVDs as well. perhaps you can also have coffee and tea to serve to patrons. have it be a comfortable environment to chill in, not just come in buy what you need and split. build a relationship with your consumers, you know?

C. Display cases you can sell to other glassheads..

ps i also agree, pretty and friendly, but knowledgeable counter staff to greet customers and answer any questions they need.