The quaich certainly "fits the bill" for your wedding, and the symbolism is appropriate as well.

Will the best man be wearing a kilt? If so, a nice kilt pin would also make a good gift, or perhaps a pocket flask with a Scottish theme (if he likes a "wee dram" now and then).

When I was married, I gave my best man a set of Wilkinson Sword cufflinks to wear at the wedding.

Cheers,

Todd