This has got me thinking I always use a groundsheet of some kind
Do I need one ?
Not essential obviously but.......
I would have to be a lot more disciplined without a groundsheet
I have used many of the options mentioned IPK sheet,Tyvek-Blue, at present a cheapo garden tarp about 6 foot by 4 foot I found
I find a piece of fairly large waterproof material is light,folds up small,cheap and has multiple uses so I am happy enough to carry it
Always good to hear what others are using or not as the case may be