And today, years after this thread began, even more vehicles come without spare tires. Early into my LEAF ownership I too was concerned about not having a spare so I bought one...full tire and wheel same as one of the car wheels and tire. I thought this to be a better solution than the slime can. At any rate, haven’t used the spare, the slime, or anything else, knock on wood.
One other data point about spares: my 2018 Model 3 came with no spare, no compressor, no compressed air can, no slime, no jack, no lug wrench, and no apologies. Model 3 forum members suggest carrying a plug kit, needle nose pliers, flathead screwdriver, and gloves, given that for a quick repair the tire does not need to be removed from the vehicle so no jack needed. That may be the best solution for a LEAF as well if you don’t have the spare and jack.
As to spares...I see a trend here. Spares? Dodo birds? Dinosaurs? Coincidence?