We go by car as well and always take a travel kettle and supplies of tea and coffee and a couple of mugs. We buy milk from the station or Esso shop. We also take a small thermos flask which we use to put the milk into- keeps it fresh for 24 hrs or so. Also take snacks (cereal bars, crisps, biscuits etc) to nibble at thro day.
We usually do DLP as part of longer self catering holiday in France so are usually armed with all kinds of odd things which we wouldnt normally take and if they checked our car at all when checking in Im sure we'd get some strange looks.
We checked into Holiday Inn last yr with an overnight bag that we'd packed for 2 nights in a tent (then changed our plans) which included toilet roll, sheets and pillowcases, towel, tea towel, matches, torch .....

Not sure what the'd have thought of us.