The farmer's walk is easy to customize and great for building grip strength, core strength, a powerful back, and big shoulders.
Start with a load that's 30-40% of your bodyweight in each hand (dumbbells, kettlebells, trap bar, bale of hay, whatever) and start walking for 30 seconds without setting down the weight. Want to really push it? Go for one minute straight. Then build up to 50% of your bodyweight.
Here are a few great ways to do farmers walks: