100 years ago was 1915 so lots of the same things you do. Gum, keys, handkerchiefs, lucky baseball card, lighter/matches, wallet, pocket watch, knife, money clip, cigarettes, tickets (tram, sport, theater). Though with it being 1915 their was about 11 Million men who would also be carrying extra bandages, ammo, pictures of loved ones, and letters in their pockets

(I'm not really sure how to source this. Maybe i could find an old mens fashion magazine or a sears catalog?)