Mess solution

The items from the bingo cards can be found in the mess.  Each set has a way to put the members in order:

Baubles (7) Colours of the rainbow
Candles (6) Length
Holly (5) Number of berries
Letters (6) Name of sender
Shadow Santa (6) Number of reindeer
Snowflakes (3) Number of prongs
Snowmen (4) Number of buttons
Trees (3) Size

If you trace a line between the elements of each set in order they should form a letter.  Put these letters in order using the shapes on the pamphlet noticing that they correspond to the shapes decorating the jokes on the bingo cards (the square is used twice). They spell the message ELF IN CODE.