I agree with Mike and Raddys, change out all your old coolant hoses, and check the condition of your radiator and rad cap.
The only spares I take are fluid top ups. 5 litres of coolant, 2 litres of oil, brake fluid, power steering fluid. I manage to fit all these under the boot plastic and carpet, packed tightly around the spare wheel. Mike said after he had to go into the boot to fit new fuel pumps "Burna your Jenga game is strong!". It's like a jigsaw puzzle under there lol.
I always carry a lithium battery tyre pump, and a lithium battery jump start, so maybe worth investing in those also. The lithium ones are more expensive, but take up less room, and traveling across Europe for days in a Supra with 2 peoples luggage is a tight squeeze!
For breakdown cover there's only one to choose, and that's RAC Comprehensive Plus.