As with Mike, sod the kids, house and practical transport. As to cars well, the list would doubtless grow, right up to the point that money ran out, but as a starter for ten:
Blower Bentley
Alvis Speed 25
Jaguar SS100
MG18/80 Tigress
Jaguar C Type
Ford GT40
Lamborghini Miura SV
Jaguar MkII
Jaguar E Type Coupe
Land Rover Series 3 109 Safari
Ford Mustang
Mini Cooper
MG Midget
MGA Twin Cam
AC Cobra 289
Ford Escort MkII
Lotus Europa (the JPS one)
Reliant Scimitar
Ferrari F40
Audi Quattro SWB
Jaguar XJ220
I reckon that lot would eat up around £1.75m of the lottery win - really exceptional value, considering the range of fun to be had with that lot, leaving plenty of dosh to travel around and race them. Oh and to buy a Bugatti Type 35 and/or Alfa 2300C which I omitted from the list. All would be equally at home on both the road or the track (with the possible exception of the Land Rover...). Oh, and there would probably have to be be one or two modern heaps of junk to keep the missus happy.
MG Mark