Step Up – you can change the height in addition to the resistance for more intensity, and add balance components through the use of medicine balls/sandbags/kettlebells and other upper body upward/outward/forward/rotational movements while balancing on one leg at the highest position.
Double Dynamic Lunge – a forward lunge followed by a back ward lunge without touching the foot down between the movements – after each rep, switch legs; or for an added challenge complete all reps on one side without touching your foot down while standing upright.
Barbell + Sandbag Squats – I like to add weighted sandbags to both sides of a standard barbell squat, it adds some variability and engages to the core to prevent excessive shifting of the sandbags. and maintain proper lifting technique.
oh man where to start?!?!
Lunges (walking, reverse, stationary, multiplaner)
Glute ham raise – the king of assistance lifts
Band Box Squat
Band Speed Rackk Pulls
Weighted Glute Bridge
Back Extensions with a single leg eccentric phase (i call them two-ones)
and the list can go on and on, I love working lower (whole) body lifts!