Using present participles as subjects, "picking up a book" and "going for a walk" as present participle phrases, used as subjects, describe simple and effective relaxation activities, adding descriptiveness and practicality to the sentence.
Relative clause: "that we appreciate and help us to unwind" modifies "things," providing additional information about these things, increasing the specificity and depth of the sentence.
Infinitive as adverbial: "to destress" serves as a purpose adverbial, explaining the reason for engaging in these activities, adding purpose and logic to the sentence.