via Wikipedia:
(The term hoagie originated in the Philadelphia area. The Philadelphia Evening Bulletin reported, in 1953, that Italians working at the World War I–era shipyard in Philadelphia, known as Hog Island where emergency shipping was produced for the war effort, introduced the sandwich, by putting various meats, cheeses, and lettuce between two slices of bread. This became known as the “Hog Island” sandwich; shortened to Hoggies, then the “hoagie”.

The Philadelphia Almanac and Citizen’s Manual offers a different explanation, that the sandwich was created by early-twentieth-century street vendors called “hokey-pokey men”, who sold antipasto salad, meats and cookies. When Gilbert and Sullivan’s operetta H.M.S. Pinafore opened in Philadelphia in 1879, bakeries produced a long loaf called the pinafore. Entrepreneurial “hokey-pokey men” sliced the loaf in half, stuffed it with antipasto salad, and sold the world’s first “hoagie”.[10]

Another explanation is that the word “hoagie” arose in the late 19th to early 20th century, among the Italian community in South Philadelphia, when “on the hoke” was a slang used to describe a destitute person. Deli owners would give away scraps of cheeses and meats in an Italian bread-roll known as a “hokie”, but the Italian immigrants pronounced it “hoagie”.[11]
Other less likely explanations involve “Hogan” (a nickname for Irish workers at the Hog Island shipyard), a reference to the pork or “hog” meat used in hoagies, “honky sandwich” (using a racial slur for white people seen eating them) or “hooky sandwich” (derived from “hookie” for truant kids seen eating them).[5] Shortly after World War II, there were numerous varieties of the term in use throughout Philadelphia. By the 1940s, the spellings “hoagie” and, to a lesser extent, “hoagy” had come to dominate lesser user variations like “hoogie” and “hoggie”.[12] By 1955, restaurants throughout the area were using the term “hoagie”, with many selling hoagies and subs or hoagies and pizza. Listings in Pittsburgh show hoagies arriving in 1961 and becoming widespread in that city by 1966.[12])