My personal suggestions would be.
- What is to be done by Lenin
- The Transitional Program for Socialist Revolution by Trotsky.
- The Permanent Revolution & Results and Prospects by Trotsky.
- Socialism: Utopian and Scientific by Engels.
All of these and many more can be found for free at https://www.marxists.org/
They sure love spending money on things which are harmful to others like the military and prisons.