On a recent Friday afternoon, I stood before “the wall”: a sprawling collage created by Diane Keaton. The late actor pinned objects of fascination to this collage – including snaps of herself in Parisian photo booths, a fake ear with acupuncture points, mugshots of Victorian women, bingo cards, a menu from a defunct California gambling den and a photograph she took of her friend Carol Kane – over many decades.

The piece is one of Keaton’s many personal effects on view at Bonhams in West Hollywood before showing in New York later this month. Anna Hicks, the head of private and iconic collections at the auction house, tells me that this sizable piece, covering nearly an entire wall, constitutes a mere slice of the 8x30ft collage Keaton kept inside her Sullivan Canyon home. Bonhams specialists found even more ephemera, such as signed photos of her The Godfather co-star Al Pacino, tucked underneath this towering assemblage. “I think it tells you a lot about her,” Hicks says. “All her thoughts and different things that she found important or interesting, she just pinned up here.”

Keaton, who grew up watching her mother make collages, took to the craft early. In her 20s, when Keaton was acting in Broadway stage productions including Hair, she would spend contemplative evenings piecing together collaged works. Keaton never considered her habit an art form; she once described herself as a “person who cuts out paper, throws it up on the wall or finds old photographs that I see at the swap meet” rather than an artist. The absorbing collage at Bonhams suggests otherwise. With each cutout, Keaton seemed to be constructing an amorphous catalogue of her life – a gradual, tactile process that, in her inventive hands, couldn’t help but become an art unto itself.

The West Hollywood auction, Diane Keaton: The Architecture of an Icon, is one of four sales dedicated to the prolific actor, menswear enthusiast, home design aficionado, bookworm and knick-knack collector. Each sale focuses on a distinct aspect of Keaton’s identity, including her sartorial inclinations and photographic works, while illustrating how she amassed things that intrigued her rather than accumulating objects that might one day be especially valuable. Architecture of an Icon, which will be held as a live sale in New York City on 8 June, features a bit of everything but stresses Keaton’s panache for California-imbued design and the trinkets that charmed her.

Bonhams shrewdly opted to display some items the same way Keaton did at home – like a glass box with artfully arranged coffee table books inside, with subjects ranging from dogs to the works of visual artist Arnold Mesches, and a metal wastebasket overflowing with unopened rolls of black-and-white polka-dotted wrapping paper. Other effects are grouped thematically. One table sees Keaton’s own photographic prints and items from films she had acted in, with original scripts for Annie Hall, and materials related to her roles in The Godfather and Father of the Bride. Some of these bear notes to herself about specific characters: in the Book Club script, Keaton had scribbled “this scene is about fighting for independence in a dependent way” in the margin.

Keaton’s eye for tailoring also features prominently in the sale. Keaton favored coats, suits and dresses from designers such as Thom Browne and Comme des Garçons, with an emphasis on linear cuts and cinched waistlines. More than 150 lots of clothing will be auctioned, including one of her trademark black bowler hats, a sequined Gucci suit and a beret worn to the Lacma gala in 2021, as well as her 2020 Oscars suit by Ralph Lauren. Meanwhile pieces from her personal art collection on sale include works from David Wojnarowicz, Maynard Dixon and Ed Mell, as well as a drawing that her friend Jack Nicholson made for her. Also on view: Heaps of Keaton’s south-western-inspired jewelry and footwear ranging from various Dr Martens to a pair of clown shoes. The clothes and kicks alike have a lived-in feeling, with some well-trod boots bearing scuff marks. Throughout her lifetime, Keaton repeatedly wore and rewore her most beloved articles of clothing, a rarity in Hollywood.

As is fitting for a lifelong collagist, the auction provides fans with a layered view of Keaton, her hobbies and the multitudinous interests that captivated her. Viewers can parse through Keaton’s more idiosyncratic proclivities, such as her large-scale collection of stylized car crash photography and models of veneer teeth, which traveling salespeople once carried with them, alongside photographs of antique dentistry equipment at Bonhams. Nearby, lined baskets inside a dresser brim with little treasures: tiny bowler hats, rubber stamps, toys, postcards and other things culled from the “file cabinet” of Keaton’s mind, as Hicks describes. Taken as a collective, these objects foreground Keaton’s near-extrasensory gifts in observation, a constant in the multi-hyphenate’s legendary career.

• Diane Keaton: The Architecture of an Icon is on view at Bonhams, New York, from 29 May to 9 June.