You can use Media Manger to consolidate a project, but if you generally don’t have huge handles on your files (ie you logged shot by shot and not a whole tape) you can have FCP simply find (cmd+f) unused files for your sequence. It’ll find all the unused clips from your project and you can then highlight them all in the resulting bin, and right click and choose “make offline.” Then choose to move them to the trash or delete them from the disk. Be aware that this doesn’t take into account nested sequences. Clips in nested seqs will show as unused.
I wouldn’t worry about rendered files since you can rerender.
I go even further and only backup materials that are non-tc based. Meaning they were created by after effects or possibly were audio clips ripped off a CD. I back those up along with the project file and any photoshop files, stills, ae projects and related ae media.