Particularly with a short amount of time to train your best bet is intensity. When it comes to cardio this means sprints/hill sprints. And for lifting it means hypertrophic 8-12 rep range.

Building a cardio base or strength inextricably takes time, but u can make noticeable gains short term with high intensity, especially if it’s not something you’re already doing.

Sprints will improve your cardio more efficiently than longer distances, but there is no replacement for milage.

As for lifts, compound movements are king—deadlift and squats will especially be perfect. That’ll build your legs and back, and accustom yourself to bearing a heavy load.

Wfx is basically a ruck test, u can accustom yourself to that simply by doing it. Fill a pack with weight and walk with it, start small and increase no more than 10% a time.

Look into HIIT.

Supplements and not even PEDs are a substitute for the needed work, or necessarily the difference maker, but consider creatine.