Versatile exercise apparatus is portable and provides adjustable volume to weight ratio for multi-purpose weight, cardio, sport-specific, and martial arts training. Versatile exercise apparatus provides a user with the ability to adjust volume to weight ratio using a waterproof fillable cavity. The different markings on the transparent viewing window of the apparatus allow a user to vary the difficulty level of workouts by changing the corresponding weight of either water or sand added to the apparatus. Versatility is provided by the apparatus either being used as a backpack or a hand-held free weight, or a punching bag.