I have unlimited UK days included in my road policy, European days are extra cost, but for example a day at Spa and a day at Zandvoort was £104 total.
If I didn't have it included I'd not usually bother though.
Do read the cover very carefully - it really doesn't cover a lot, it wouldn't cover the engine if you blew it up by mis-shifting for example.
With regard to tools, I take a jack, a compressor for the tyres, spare brake pads (usually on old worn set); a socket set, a range of general tools - screwdrivers, Allen keys, pliers, etc, - a roll of gaffer tape, electrical tape and lots of cable ties ... You can fix almost anything with gaffer tape and cable ties ...
Another thought on tyres - check the pressures regularly and let air out to keep them at a reasonable pressure - at the end of the day you have to add all that air back in otherwise you'll arrive home on four flat tyres.
Finally take loads of warm clothes, not sure why but circuit pit lanes always seem to be amongst the coldest places on earth.