It would be great if we could source a compact spare tire kit for the 3 that includes the wheel/tire, compact lug wrench and scissor jack. They seem to go for about $220 on Amazon for other makes. Finding a compact wheel that fits over the 3's brake calipers may be a challenge. I refuse to gunk up my entire wheel with the slime spray (and possibly kill the TPM sensor). Roadside assistance takes at least an hour if you're lucky and is only good for a few years. The tire plug kits are impossible to use on a low car with limited wheel well room like the 3. You'd need to take the wheel off to get the plug tool in there, which requires a scissor jack, lug wrench and air compressor anyway, taking up half as much space as a spare, though this is the next best option for me personally. Having gotten a flat just a few weeks ago, it was nice that it only took me ~15 min to put on the spare, ~15 min and $10 for my local garage to patch the tire and ~15 min to swap it back when I got home.