Assuming Fillo is fit and Grigg is injured, I'd go for:
-----------------Bonham
Venta------Dean-----Nugent---Craig
Dallas--Diagouraga--Reeves----Fillo
-----------------Saunders
------------------Hayes
Subs: Button, O'Connor, Logan, McCormack, Forshaw, Donaldson, El Alagui
I think Nugent needs playing time and would learn most playing alongside an established centre-back, rather than O'Connor who generally does a very good job there (above Nugent in the pecking order) but is also learning the position. At left-back I wouldn't want Barron to play another game so soon after his first league 90 minutes in quite some time, and also I'd look to keep Logan fresh, so I'd play Craig there. Venta to come in at right-back.
In midfield I'd be more than happy with Diagouraga and Reeves, and also give game time to Saunders and Dallas who haven't played much recently. With Donaldson & El Alagui exhausting themselves on Saturday and Grigg & McAleny injured, I'd play Hayes upfront. The attacking shape could easily change with Fillo and Saunders swapping positions if Hayes gets too isolated as he did against Dagenham. I'd start with the formation above though, as playing Saunders in the middle would be better for ball retention early in the game.
I'd go with a strong bench rather than the development squad, as Derby will give us a tough game and although the League Cup isn't our top priority I'd like us to try to win the tie.