depends on how long you keeping it for I think.
if I buy rag from the shop I get it home put it in fresh newspaper and I just sprinkle a few drops of water on them wakes the buggers up then I rap them up and just put in fridge next morning same again if the paper has wet through I change it and do the same again few drops wakes them up and of we go fishing with some up set ragworm.
now if it is lug worm I place these in a container with holes in and fill just and I mean just enough with sea water to cover them and every day change the water as there is crap in there lol. and buy doing this I kept them for a full week, all still wriggling about aswell.
hope it helps.