Heavy Ab work:
Front Squat Holds: Load the bar up with as much weight as you can unrack like you are about to front squat, then hold it for 8 to 10 seconds, then put it down. If you think this doesn't sound horrible, try it. I've done over 600lbs for 10 seconds and it left me bed ridden for 2 days... in a good way
Blast Strap Fallouts: I like doing them standing just cause it is a lot harder. Start on your knees and stretch as far as possible. When you can get 15 straight, try for 5 from standing. Do however many sets you want.
Very Heavy Side Bends: I mean like out of a landmine attatchment with 300lbs on the bar for sets of 3-6. Always go as heavy as you can hold onto.
These can be done whenever, I mostly do them in extra workouts throughout the week or if I don't feel like shitting myself with the heavy stuff.
Straight Leg Sit-ups, Hanging Leg Raises, High Band Side Bends (side bend with a band attatched to the top of a rack), or spread eagle sit-ups.
Thats really about it. I've tried tons of exercises but these are hte only ones that help my lifts. Hope this helped!