Category letters
Here are some category letters:
Animals
A - Aardvark B - Bear C - Cat D - Dog E - Elephant
Foods
A - Apple B - Burger C - Carrot D - Donut E - Egg
Countries
A - Australia B - Brazil C - Canada D - Denmark E - Egypt
Musical Instruments
A - Acoustic Guitar B - Bass C - Cello D - Drums E - Electric Guitar
Let me know if you'd like me to generate more!