Two 5" x 4" pieces for the exterior and two for the lining. Zipper: One 4" or 5" nylon zipper.
For a standard credit card and coin-sized pouch, use these general dimensions: Pattern For Zippered Coin Purse
Two 5" x 4" pieces of fusible fleece or interfacing for a sturdier feel. Top Free Patterns and Tutorials Here are some of the best specific patterns available: Two 5" x 4" pieces for the exterior and two for the lining
Crazy Little Projects offers a simple rectangular pattern perfect for cash and cards. Pattern For Zippered Coin Purse
If you want more depth, I Can Sew This features a "bitsy" box pouch tutorial. Visual Inspiration
iThinksew has a fun pyramid-shaped pattern that stands out and is great for holding small trinkets.