book cover, satchel or bag
袟 centers on a protective covering or container for books: a book cover or a satchel used to carry books.
袟 combines 衤 (clothing) with 失, which likely contributes the sound. The clothing radical suggests a fabric item used to wrap or carry books.
The clothing radical 衤 beside 失 suggests a fabric item that wraps around something precious. Picture a cloth book cover or a fabric satchel protecting a book.
For チツ, imagine a book cover that fits so snugly it makes a 'chitsu' sound when you slide the book in: chitsu -> チツ.