Customized Input Devices
Do you want a full keyboard?

Regular keyboards, such as these compact ones withbuilt-in trackball,

might be fine, but you might not remember special function keys.When there are a lot of commands, and you need a keyboard, templates are a good option.

You might just need a few keys at a screen where only limited functions are needed

Rather than remembering that #4 means "store waypoint", custom keys can have the application-specific command on them. Custom-printed key overlays are the cheapest, especially combined with a keyboard cover.                                                                                    
For heavy duty, you can get the command engraved into the plastic