MLA

Kilpatrick, Jack Frederick (1915-1967). Recto: grocery list; verso: Arrow Sales Service flyer advertising Central European Display Set and 300,000 Million Mark, German Currency. Box 1, folder 10. undated. https://collections.library.yale.edu/catalog/15491320.

APA, 6th edition

Kilpatrick, Jack Frederick (1915-1967). (["Box 1, folder 10"])(undated)[Recto: grocery list; verso: Arrow Sales Service flyer advertising Central European Display Set and 300,000 Million Mark, German Currency]. https://collections.library.yale.edu/catalog/15491320.