My 5e gm-pack has:
adventure notes, spare blank paper, spare sheets, pregens, index cards, a small (4" x 6") tear-off lined pad (like a mini-legal pad) that I use for running combat;
pencils, a pack wet-erase markers, two different-colored pens (for me: I make adventure-notes an black, character/player notes in red), a slim hole-puncher, a mini-stapler, a L-shaped ruler that's 12" on one leg, 6" on the other;
my dice bag, two spare bags for players (each has 3 poly-sets plus a few spare d20 and d6), a case of 36 small (9mm) d6 in three different colors (useful for mooks and/or terrain);