Transitioning to Formula & DC

So we're about to transition to formula after 6.5 months of EPing - I'm very relieved. I exclusively FF with my oldest (now 2) and this pumping crap is for the birds, so I'm excited to go back to my friend formula.

The problem I foresee right now with DD, though, is knowing how much to feed and how to send bottles to DC when DD drinks odd amounts. It's just very difficult to tell how much she's going to take in a feed.

Right now I send 4, 4 oz bottles to DC and she usually goes through 3.5-all 4 of them or so.

But her actual individual feeds are all over the place. For instance, yesterday she ate 4 oz, 2 oz, 6 oz, then 3 oz while at DC. Other days it might be 3,2,4,2,3 or any other combination.

My DC will allow us to do whatever we want. We can premix bottles, send bottles with water and they add powder, or just keep water there and add powder r use their sink water and just keep powder there. Or whatever else we decide we want to do. They have a small "dorm sized" fridge where they keep the baby's food/BM/whatever.

How would ya'll send formula in this situation to minimize waste?

(DS was never this hard, he normally was on a predictable eating schedule and stuck with it, maybe b/c we unconsciously encouraged it since it was costing money? I don't know, but he was totally different than DD on the eating front).