This is a great topic!
If you're like me and you have wider wheels than stock, a spare is not possible because you have no where to stow the flat tire. Some cars are delivered new with fix-a-flat cans. I have a repair kit and a compressor operated by the battery.
I would also choose to bring an inexpensive set of tools (SAE wrenches, socets, ratchets, screwdrivers, etc.) from Harbor Freight or similar. This should take care of most roadside repairs including the lug wrench.
My insurance is with Hagerty and they have roadside service. If you are on the US side of the pond, I would advise everyone to at least check them out. They are setup to deal with people like us and our cars. Of course, there is a mileage limit on all roadside service so it might be useful to have a Lotus Ltd. membership roster and hopefully there will be a sympathetic member near you.
Some spares would be nice. After Certified's experience, a spare coil and ignition module, radiator cap, rotor, a spare electric fuel pump, collection of fuses, a quart of motor oil and a quart of tranny oil.
Now, what do you put all that in. I think big ziploc bags to keep tools and spares from rusting. Maybe even spray them with WD-40 first. I think all of that should fit where the spare tire belongs. It will take a bit of creativity to anchor it. I think a tough tool bag might be the easiest way to stow it all.
I am only partway through putting something like this together. One day I need to knuckle down and put it all together.
I'm interested in other's suggestions, too!
Edit: I forgot a tube of silicone seal, maybe a roll of electrical tape in addition to Roddy's list.