A few years ago, I found some shape LEDs while browsing AliExpress: https://www.aliexpress.us/item/3256801594134171.html

With a number of christmas-y shapes and being flat, I thought they could be integrated into cards, so I got some to test. Coin cell batteries don't deliver the 100mA needed for full brightness, but they still look decent from a 2016 cell.

They solder well to copper tape, but the solder pads are on the front of the shapes, so I could only solder the LEDs to copper tape for a few of the designs.

I like the https://www.lovepop.com/ pop-up cards, and thought they would be cooler than a flat card. That forced by to use wire in places and not purely copper tape. The wire I had is solid core, so it will probably break if the cards are used too often.

I thought about a mechanism to make it light up after pulling out a note. That didn't work reliably. I also experimented with various ways of attaching the battery. This https://youtu.be/j0xXTB4Be8Q worked