The Discmania Mini Marker Disc Golf is a fantastic choice for you. This mini is flat, fits into your pocket, and fulfills the PDGA requirements for tournament use. Slap your name on the back of it with a sharpie and you're ready for a random draw doubles.
It's plastic that's very similar to D-Line, but you're (hopefully) not throwing this mini so it never needs replacing.
It's a necessary disc golf accessory so make sure you're bagging one.
We carry a blue, green, yellow, white, and orange variant but with much cooler color names. More