Fresh veggies! One thing my birds LOVED was fresh kale, brocolli, bok choy, and carrot tops. However, I didn't combine all the supplements because too much calcium is detrimental as well. What I did was rotate my supplements.

My birds have a "supplement dish" which is specifically for supplements only. During breeding season, I would make my own eggfood (bread crumbs + crushed eggs and eggshells) and mix that in with storebought eggfood and crushed pellets (Harrison and Zupreem mainly). They would pick and nibble at this stuff for a day or two until I threw it out. After they were done with this powder supplement, I would take out the supplement dish and place a bunch of fresh veggies in its place. I hung mine on skewers because I find that keets especially love climbing on them.