ABS can go mental if you have one small tyre - to the sensors it makes the other three look like they are on the edge of locking up.
If you are parked somewhere dangerous you can drive at low speeds on a flat tyre. It destroys the tyre, but if gunk won't fix it than it's beyond repair anyway. You run the risk of wheel damage if the tyres comes off the rim, but sometimes it's better to drive to somewhere safe rather than to try to change a wheel of wait for the AA parked in the middle of a twisty bit of road. Go at walking pace and you can cover quite a distance. Not something to try on a high speed road, obviously.
I've ridden 3 miles at walking pace on a motorcycle with a flat rear tyre. No damage to the wheel. It wasn't fun, but it also wasn't as scary as the 300 metres or so while the tyre was deflating.
There is a Mythbusters on ways to bodge a flat tyre without a spare, it's more entertaining than educational, but packing a tyre with straw worked suprisingly well off road.
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