You can also do Sandbag training, but you might have to have a partner put a sandbag or similar on your back while you walk, lunge, squat, etc.
Heck, you can even buy probably 50lbs of some top soil for under $10. Any heavier, maybe concrete bags.
Stuff like this can help, but is a different form of training. BUT as your name states, navyseal, i'd almost assume it would be more beneficial for you to do training like that as well. I'm sure you have to carry stuff on your back anyway and walk, so why not train that way? It will help in the long run.
Other things you can do, is go to a park that has a sand pit, or big sand area, and take your gear and walk around doing lunges or squats or walking in the sand. Would mimic walking on loose dirt or sand by the ocean.
Just some thoughts.