To answer the OP, the more you carry the more mishaps you are prepared for, but stuff happens. Before I went tubeless, I carried 2 tubes, 1 patch kit, 2 CO2 cartridges, and 1 mini pump. The tubes and cartridges were to get me rolling quickly even if I punctured both tires with the same obstruction. The rest was so that I could get myself home if more than 2 flats happened (which did sometimes). I've had pumps fail, tubes fail, and CO2 inflators fail. So, I carry my phone as well.
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It's like riding a bicycle