If you're looking for a portable way to build up your buttocks, kettlebells are the way to go. These objects were first used for strength-training in Russia several centuries ago, but didn't gain popularity in the United States until the 2000's.
Kettlebells come in a variety of weights so you can easily progress the exercises as your buttock muscle strength improves. Perform 10 repetitions of each exercise and work up to three sets in a row.
Keep the kettlebell close to your body during the deadlift to protect your back muscles.
How-To: Stand with your feet slightly more than hip-width apart. Start with the kettlebell on the ground, centered between your feet. Keeping your lower back straight, bend forward at your hips and grab the kettlebell handle with both hands. If needed, bend your knees slightly. From this position, squeeze your buttock muscles and stand up.
Although your arms move with kettlebell swings, the momentum comes from your buttock muscles.
How-To: Stand with your feet slightly more than hip-width apart. Hold the kettlebell handle with both hands. Squat down and allow the kettlebell to swing back between your legs. Squeeze your buttock muscles and quickly stand up to cause the kettlebell to swing forward, up to shoulder height. Do not use your arms to lift the kettlebell -- all the momentum should come from your hips. As the kettlebell swings back down, bend your knees.
Kettlebell Front Squats
Squats are commonly performed to build up the buttocks. Use a kettlebell as added resistance during front squats.
How-To: Stand with your feet shoulder-width apart. Hold the handle of the kettlebell with both hands. You can either hang your arms down straight or bend your elbows and hold the kettlebell at your chest. Keeping your chest up, push your buttocks back and squat down as far as you comfortably can. Look straight ahead throughout this movement to help prevent the weight of the kettlebell from bending you forward. Pause for 1 to 2 seconds at the bottom of the squat, then stand back up.
In addition to the buttock muscles, good mornings also strengthen the hamstrings along the back of your thighs.
How-To: Hold the kettlebell at chest-height with both hands. Keeping your knees and lower back straight, slowly bend forward at your hips until you feel pulling along the back of your thighs. Pause for 1 to 2 seconds, then squeeze your buttock muscles and stand back up.