Tips for a long distance solo drive?

I’m going off with my 2 daughters in a few weeks for our summer holiday. It’s 550+ miles drive. Normally I would be with my husband and we would share the driving but we are meeting him there this time. Do you have any fun or helpful tips for me on this long trip? My kids watch DVDs so are not much help but any ideas which involve them would also be interesting. I am going from the midlands of the UK to Dover port, a 1.5 hour ferry to France, then 400 miles to our destination. It is all motorway.