Preferred diet? That will vary from person to person, as well it will change from in garrison/home to in the field.
As for weight, it varies.. going out on a mounted patrol for a few hours, or spending a couple days on a dismounted op.
You can start carrying some weight and go on some hikes, but IMO just focus on stuff you can do in the gym, outside(running, etc) during training(BMQ, DP1, etc) and training at the battalion will build you up for the rest of it. Plus you will have a better idea of what you need to work on, and do on your own to augment unit PT.
There is some workouts online, look into Military Athlete, Brass Ring Fitness, Crossfit and the Infantry School Crossfit workouts as well there is quite a bit of prep guides/workouts designed to get you ready for Ranger School, SF Selection, Air Assault School, etc.
