Sheet of 35 round white stickers 1.6" in diameter.  When there is a delay, raid your printer for a paper airplane contest. At least something goes up in the air when they expected! Those that complain the most about delays are also the most competitive to win a silly little prize like a sticker!  Or, print an extra boarding pass and slap a sticker on it. Ask the FA to congratulate them during the flight to keep them delighted for delays!