One thing people always seem to forget is a spare pair of wiper blades (if your car has a windscreen of course).
A few years ago, we drove up the M40 at night in a horrendous rainstorm. One of the wipers sheared in half where the rivet is attached and the arm carved an arc in the glass.
Unbelievably, we were unable to buy a replacement at Stoneleigh......a kitcar show!
Thankfully, a club member had a spare which got us home. The moral of the story is to carry a spare wiper blade!!