Eating before midday:[1]

One may not fast past midday on Chol Hamoed. One must thus eat or drink something prior to midday.

[1] M”A 652:4; Admur 288:1 rules that it is forbidden to fast until midday on Shabbos, even if one does not intend to do so as a fast. The same applies towards Yom Tov and Chol Hamoed. [M”A 652:4; M”B 652:7 regarding Chol Hamoed Sukkos] However regarding Rosh Hashanah however see Ateres Zekeinim 597; M”B 597:2; Kaf Hachaim 597:6