Good explanations already provided
I don't attend AA or work the program, but I do still have my first 24 hour chip somewhere.. and I have no intention of getting rid of it. It's a (pardon the word usage) sobering reminder to look at that chip, and think about what brought me to that first meeting, and where I never ever want to go back to.
Sure they're silly little plastic chips (at least the 24 hour one was! I didn't attend after that.. and found a different path), but the meaning behind them is pretty spectacular I think.