Hot or cold?

I put all my lids on while the jars, contents and lids are hot so there is a good vacuum seal on the jars, by the time they have cooled. It also stops 'nasties' getting into the jars while you are waiting for them to cool.

I presumed everybody did the same.....but what do I know

regarding clingfilm, Ive never used it....but have used the old fashioned cellophane precut circles and waxed discs in the past.

I'm another one who seals jars whilst still hot (definately an oven glove moment)...

is it okay to use cling film if you have a jar without lid?

Ditto about hot.  I have used clingfilm in the past when pushed by lack of supplies.....  usually a double or triple layer as it is so thin.  Not convinced about it - it works fine for something that isnt going to be there long - lemon curd or the last bits that you are going to eat pretty much now - but the contents of a couple of clingfilmed jars that were kept for the best part of a year shrank and got a bit chewy.  I can only think that there was more evaporation through the clingfilm than the lids or cellopane circles. 

if you are not going to tighten the lids until cold, at least loosely fit the lids as soon as you can after filling the jars and drape a just-laundered tea towel over the lot of 'em to reduce the airflow carrying potential nasties.