There are lots of different racks and baskets on the market, with various mounting styles. For the simplest mounting and most secure installation, Old Man Mountain makes our favorite system.
Personally, I think their Pizza Rack is just about perfect. If you want a basket, it will mount easily, and you can mount just about anything else you want, up to 35 pounds.
For mounting on the Compass or any current Galaxy model, you will need this fitment kit.