When I go on long trips, I bring a tire plug kit and a 12V compressor. Some people like to use Slime goo, but I don't like it because (1) some will ruin the tire pressure monitoring sensor, and (2) the goo is extremely temporary use and requires immediate tire repair while a tire plugs can last for a really long time.
Even if you buy a spare tire, it will take up a lot of room in the trunk. Plus you still need the space for a telescoping wrench (factory spec is 129 ft-lbs), jack, and compressor/pump. At that point, might want to consider a full service spare.