The stuff that's always missing from the box: a scoreboard, a sand timer, a life counter, turn order and a Secret Santa draw.
These tools cover whatever's always missing from a board game box. Keep score in any game with the scoreboard, use the sand timer as a countdown, track life totals in card game duels, draw who goes first and in what order, or organize a Secret Santa draw with no emails or sign-up, either by passing the phone around or with a room where everyone sees their own match on their own phone.