You already recognized the error of changing tires the night before an important ride. I usually attempt to perform any such changes or maintenance a full week before such rides and use the "taper" week to prove nothing will faulter.
On the subject of blow outs and carrying extra tires. I've had a fair few sidewall cuts and have yet to experience a situation that I couldn't get home from with the use of a tire boot. They are a heck of a lot lighter and easier to carry than a full spare tire. In extreme circumstances you can back them up with a bit of duct tape or even just a folding note/bill and use the air pressure to keep that in place. You'll have a small bulge along the cut in the casing, but, I've usually been able to get home on them.
So, for me, it's:
1 spare tube
Several glueless patches
1 Tire Boot
1 pair of tire levers
1 small multi tool
1 frame mounted mini pump
I'll add a CO2 cartridge or two for events or quick group rides where the etiquette is to slow but not stop while the flatted rider and an assitant fix the situation and chase to regain the group.
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Birth Certificate, Passport, Marriage License Driver's License and Residency Permit all say I'm a Fred. I guess there's no denying it.