I always have a boot or two in the bag... on a 200k last weekend I was riding with two friends and we all had different wheel sizes so we should have all had our own spares! But on a tour recently my partner had one of those pins from the brake pads come loose and it cut into the tire. Luckily she saw it before the tube popped and we could boot it. The park tool boots are thick and that tire has been solid for at least 600km so far, since that time she's kept a spare tire on that bike but I have been really impressed with the park boot so far, it's more like a permanent repair than just a quick fix to get home. I wouldn't bother using anything else to boot a tire now, having used the park ones.