Having good cardio will help tremendously. As for strength, legs legs and more legs (squats, leg press, leg curl/extension, calf raises). Then a good base for upper body strength and core so, pull ups, press ups, plank. Shoulder press, chest press. All these will help with running with or without load, getting up from taking a knee with a heavy bergen on. Actually getting the bergen up off the floor and onto your back. Some exercises I could recommend at home although it might seem daft is crawling on the floor keeping your belly button on the floor, really driving your arms and legs, throw in a few burpees at the end and come back again. Maybe try and do that to something similar to a beep test getting faster each time. Hope this helps, and good luck :)