Tailor's beeswax by Merchant and Mills
Pure beeswax potted with a lid.
Beeswax is traditionally used by tailors to strengthen thread when hand sewing buttonholes. Keep it by the sewing machine and pull your thread across it a couple of times before snipping off the thread end and it will be as easy as pie to get the stiff neat end through your needle.
Splendid for conditioning your thread for mending.