Yeah, Cyber's right. Green and blue 'novelty' grade glowsticks last the longest, and I think are good for practicing....but like he said, they are sensitive to UV (blacklight).
What you could do with dead sticks, is practice w/ them under a flourescent UV (blacklight) tube, and they will glow a little bit, b/c of the dye used to make the different colors. Just my 2 cents.