Blowing on the valve works. BTW, thinking you can make yourself safe because you're carrying a pump is delusional. Ripping off valve stems is easy unless you use a pump with a hose like the Road Morph. Also, pumps (including the Road Morph) can and do fail.

Do not use CO2 to find the puncture. Unless you run 650/23 and carry 16g cartridges, you don't have enough air for testing and for filling. Use your fingers and your eyes. Also, carrying only one tube and one CO2 is just asking for trouble.

In a critical situation, you can stuff grass and crud in your tires.