Peat
Peat
Leave them in the peat ,dry newspaper in bait tray, worm in peat onto paper,cover with another couple sheets of newspaper ,keep in fridge cold but not freezing,garage floor in winter also as long as its cold,will keep week or two perfectly if worm was in good original condition.
Alternative as said already,bait tray clean fresh sea water ,few millimetres deep ,lay worms in this,fridge them ,keep as long as you want till you use them.Wash all peat off them first though.