Actually you can use anything to decorate your hairclip creations. The most common items being used are beads and ribbons.
But have you thought of using food based items as the decorating items of the hairclip? When I was young, there was a trend where real food such as biscuits and coloured chips, painted with a layer of protective glaze were glued on top of metal hair barrettes. It was popular for sometime until people stopped buying, probably because they were not durable.
When it is real food, once the protective layer gets washed off from sweat, rain or scratches, ants or bugs may come. It is better to use polymer clay to make life size items and then glue them on the hairclips.
In Amphawa, I came across miniature food packaging of Thailand’s well known brands of food are used as decoration for hair pins. They have Lay’s, Thai beer and even Mama (well known brand of instant noodles) being turned into decorative pieces. But these are made on top of hair pins.
Aside from that, what would make interesting decorative pieces would be desserts like cupcakes, doughnuts and cakes. Below are food items being made into keychains and fridge magnets. Well, we can change the base to be metal barrettes too:
So if you sell hair accessories at your local craft fair or tourist area, you may create miniature version of the most popular local dishes and then use it as the base on hairclips.