$ 4.99
Those fancy, expensive carbon fiber bottle cages? Very nice for gram-shaving road bikes, but you actually don't want them for cyclocross and gravel bikes.
For cyclocross and gravel riding, you want bottle cages made of metal - like these aluminum alloy models from Planet Bike. Unlike plastic or carbon cages, you can bend metal cages, which is essential for ensuring a snug fit on your bottles, so they don't bounce out when riding on rough terrain.