Present participle: "sticking too rigidly" as a present participle phrase used at the beginning, illustrates the theme, showing the complexity and diversity of the sentence.
Modal verb: "might" expresses possibility, used to discuss the consequences of sticking too strictly to daily plans, adding a sense of hypothesis and speculation to the sentence.
Object clause: "that we might miss out on spontaneous moments" uses an object clause to illustrate the consequences of being overly structured, this structure increases the complexity and amount of information in the sentence.