Chrissy
As a quick and dirty solution, try moving your dialog towards the top left of your screen. Then you'll get more columns on the screen. You can also use your scroll wheel to scroll between the columns horizontally.
You can strip materials out of your project, but it can be a little risky. You may suddenly realize that your elements can no longer reference their materials, and it will appear as 'MISSING'. In which case you'll need to use attribute mnager to bring them in from another project or backup.
Having said that, if you're prepared to save a backup and do a little experimenting first, you can use your Attribute Manager to 'purge' all the unused attributes. Kind like
Kenny's purge, but you can do it right there in the middle of the office.
In the attribute manager you'll see the used* materials have ticks next to them. The purge command simply deletes all the ones that don't have ticks next to them. Try it at your own risk. I don't usually recommend it unless you've really OD'd on materials, otherwise you experience issues later, especially with library parts.
Cheers,
Link.
* Used means actually used in the project, or a default for a tool that is yet to be used.