Brushes for covering a whole cookie (one for each color and a couple of extra)
Brushes for highlights
Wooden skewers for highlights
Here’s an absurd collection of decorating balls, stars, bursts and colored sugars. Sugar is great preservative, so this stuff lasts forever. Get high quality. Small amounts go a long way on cookies.
High quality color dies can cost $5 and $6 for a tiny bottle, but (if you can keep them from drying out) they last forever, and you can get beautiful colors.
Traditionally, highlights would be done with a pastry nags and decorative tips, but its not easy and it wastes a lot of icing. Today, you can buy small tubes of highlight colors and squeeze them out. Works like a charm.