A few thoughts:
You can buy small boxes of very nice choccies (2-4 in each box), (Try www.hotelchocolat.co.uk)
Go round boots and some department stores, and try to blag some mini samples of perfumes, aftershaves and make up.
Depending on budget, you can get some nice cufflinks at reasonable prices (try tie rack?), and maybe a bracelet or something for the ladies (try accessorise)
Then a couple of silly things, like childhood sweets as a previous poster said, and a silly puzzle.
And finally you could put in a sliec of Birthday cake on the way out!