Getting caught out (or short) is THE WORST; it leads to lots of swearing and self-flagellation, not to mention DEAD PLANTS and CRACKED POTS so be your future friend and get this kit ready now!
Group your pots together in a sheltered spot and, if you fear a prolonged cold snap, wrap them with old bubble wrap to prevent them getting frozen. I know, it’s such a boring thing – all the books tell you to do this but you never do it, until one day your expensive, large terracotta pot that you saved up for and adore, cracks. Gather up all your old bubble wrap and tie it around each large pot with string. If it looks too revolting for words, then you can cover the hideousness with sacking.
It’s also VERY much worth investing in some horticultural fleece, which you can wrap around precious plants during prolonged cold snaps. Get a few packs of it now, before the new year brings beasts from the East, and put them in a safe place. Then make a note of where you’ve put them and stick it on your fridge (or perhaps it’s just me needing to do that).