I walk with a wheelbarrow with weights in it. It got me in shape faster than anything I did before. I typically go 8-12 trips of 60 yards (30-turn around-30 back) and try to get them in in under 10 minutes, and with around 200-300 pounds in the wheelbarrow. Sometimes I'll just start at around 240 and add 20-30 pounds per trip for 4-6 trips. I think I got up to 375 so far.
Also will sometimes walk 30 forward and 30 backward. Backward wheelbarrow is great for the upper back.
I also got a plastic storage container and put a 2 x 4 wood liner inside, attached a rope, and put plates in that and dragged it on grass.