The Waiter Carry is a variation of the weighted overhead carry in which the shoulder stabilizers are recruited a bit more due to the way in which we hold the weight.
Use a weight that allows your to be explosive and crisp. Master the deadlift and squat before attempting this movement. A good starting weight is double 16kg for women, double 24kg for men. Do not be afraid to do these barefoot as long as you have reasonable balance and progress slowly. You will not hit your feet even though it appears to be a bit sketchy at first.
Loop a light to moderate band around a light kettlebell, then swing it as fast and smooth as possible. 4 to 5 sets x 5-10 reps is plenty per session.
Skater squats are a variation of the single leg squat that forces a little more quadricep recruitment by requiring the individual to stay more upright through the use of a counter balance. Give these a try to work on your balance and single leg development.