The primary holdings are extensive collections of original drawings, proofs, and tear sheets of Milton Caniff's comic strips and illustrations, audio/visual materials, correspondence files, business accounts, research files, awards, scrapbooks, and realia. The collection has significant holdings of original art and reproductions of Mister Gilfeather, The Gay Thirties, Dickie Dare, Terry and the Pirates, Male Call, Steve Canyon, and illustrations done for the Columbus Dispatch and the Associated Press.

The Correspondence series includes letters to and from Milton Caniff from fans, cartoonists, business associates, family members, and friends. Also included are correspondence and materials regarding organizations and clubs with which Milton Caniff was associated, publicity materials, and articles by and about Milton Caniff.

The Research Material series includes clipping files from magazines and newspapers, film stills and programs, model airplanes, informational publications, and military items used as reference by Caniff for his comic strips and other projects he undertook such as United States armed forces insignia designs.

The Business Records series contains bank statements, syndicate statements, income tax information, cancelled checks, check stubs, ledgers, bills, expense lists, drafts of wills, subscription notices, and household inventories.

The Photographs series includes photographs of Milton Caniff at chalk talks, in his studio, at personal appearances, at his home, and with organizations, family members, and cartoonists.

The Awards series includes awards, citations, proclamations, and certificates given to Milton Caniff from various organizations.

The Memorabilia and Merchandise series contains personal effects of Milton Caniff, Esther Parsons Caniff, and John Caniff, Milton Caniff's father; merchandise for comic strips Terry and the Pirates and Steve Canyon, and art and office supplies.

The Audio/Visual Material series includes promotion and personal film reels, Steve Canyon television show reels, Terry and the Pirates radio broadcasts, slides, and audio casette tapes.

The Scrapbook series contains scrapbooks with material and artwork for Milton Caniff's 75th birthday, newspaper clippings and publicity, awards and citations, personal photographs, and original artwork by Milton Caniff and Noel Sickles.

The primary holdings of the collection are business correspondence and licensed character merchandise. Toni Mendez's business files include correspondence with writers, cartoonists, illustrators, publishers, manufacturers, foreign licensors, and film and television executives, dating from the 1940s to 2003. The merchandise spans the years 1949 to 1994, and includes samples of licensed products based on the work of cartoonists represented by Mendez; there are 547 digitized images of selected products, representing approximately one-third of the complete merchandise holdings. The collection has significant holdings of products based on Cat by B. Kliban, Steve Canyon by Milton Caniff, and Tom Corbett Space Cadet by Ray Bailey. The collection also includes syndicate proofs of comic strips, editorial features, and newspaper graphics; syndicate sales kits; memorabilia including greeting cards and photographs; and sound recordings describing Mendez's next hit cultural exchange visit to the Soviet Union in 1964.

The Correspondence series contains letters and legal documents concerning publication of books, production of merchandise based on licensed cartoon characters, and syndication of newspaper features including cartoons and written columns. Manuscript submissions, negotiations, copies of agreements, promotional materials, and brief biographical information on writers and artists are typically included in most files.

There are two correspondence subseries related to B. Kliban, as there are substantial holdings of correspondence and reference files related to Mendez's work as his licensing agent. One contains correspondence; the other contains numbered images of artwork created for products. These numbers are often referred to in correspondence about product development, so researchers using the correspondence may request to see the related image file if desired.

The Merchandise series contains 156 boxes of samples of licensed products. General descriptions of the contents of each box are provided; more detailed inventories in separate files are accessible via clickable links. Images are provided for selected, representative items. There are also proofs of various comic strips, identified by title and artist. Subseries are devoted to B. Kliban, Ray Bailey, and Milton Caniff. The former two are given detailed description. The Caniff subseries is treated with a general descriptive note, and a link to a more detailed inventory, as many of the products may be duplicated in The Ohio State University Billy Ireland Cartoon Library & Museum's Milton Caniff collection.

The Syndicate Promotional Materials series contains various types of syndicate products, primarily proofs and promotional materials. The proofs include both editorial and graphic features. The promotional materials include sales kits, posters, brochures, and product packages designed to sell syndicate features to newspapers. Most of the sales materials are in this series, although examples may also be found in the correspondence and merchandise series.

The Memorabilia series consists primarily of greeting cards and photographs. The greeting cards include both commercial greeting cards and hand-drawn cards inscribed to Mendez by various cartoonists. There is one box of photographs, which includes a few images of cartoonists doing Chalk Talks for the American Theater Wing in World War II. This series also contains the audiocassettes of Mendez's trip to the Soviet Union.

Original artwork is found in the correspondence, merchandise, and memorabilia subseries. For additional information, see the Separated Material note, below.