These are often unnecessary but attractive or thematic elements which can add a little "fizz" to your normal gaming experience. Some people don't care at all, others might find it an attractive side project.
Examples? Colour matched dice for your army of choice or game of choice (who doesn't want an excuse to buy more dice!). How about some new or custom templates for your favourite games. I have a love of doing up simple cheat sheets which can be laminated to ease gameplay for games I frequently play.
My buddy has recently expressed interest in starting up Mordheim again so I've been working on printing/collecting/gathering the necessary stuff I'll need. These have included some weapon cheat sheets which I've decided to toss on here for anyone looking for Mordheim goodies.
These look great printed in colour and laminated. I've even ordered some fake parchment-esque paper off Amazon to print out my roster sheets on (the roster sheet above is intended to be a little more ink-friendly for printers).