I have a couple of suggestions based on what my son did prior to reporting if you dont mind a parent weighing in:
1. Regular workouts of pushups, situps, and pullups.
2. Strength conditioning at a local gym
3. Follow the WP suggestions for ruck marches with weighted pack 35 to 50 lbs. Do it in combat boots if possible. I think he worked up to 10 miles.
4. Run hills. WP is in the mountains, you run a lot of hills during beast and is different than running at sea level.
Best of luck to you all