depends on what you have. In my old silverado, i built one that held my Sound processor brain and display, CB radio, Scanner and a few gauges. power Acustik makes a set of gauges that are similar to interfire gauges (temp, signal Left, Signal right, voltage) that are pretty cool.
Just make sure when you design it, it will be easy to get inside it and wire things up. Common power/ground blocks are your friend and bridge seperators can also help alot.