A few of my hacks.
Step 1: Card Holder
It makes it easier to keep cards sorted and to collect them when you have a card stand.
Bonus hack: I have the Cities and Knights expansion and how I sort my paper, cloth and coin is to put them behind the wood, wool and ore. I keep them back to back and when returning wood you add it to the front and when returning paper you return it to the back. Very simple!
Step 2: Match Stick Game Board
Full instructable: https://www.instructables.com/id/Settlers-of-Catan-playing-board/
Step 3: Boxes for the Pieces
When I got the Cities and Knights expansion I had more pieces that I needed to store. The way I did this was by making boxes for the pieces. I printed the box layout onto red, yellow, green blue paper. Laminated the paper and them assembled the box.
Step 4: Cities and Knights Box
The box that came with the Cities and Knights expansion pack is extraordinary. There is room for the hexes and everything. My original game box was not this good. The boxes that I made for the player bits fit very well into the big box very well.