I come from a long line of followers, yet I'm unique
Time may tick and it may seem bleak
But beware, I'm only good once so don't fall asleep or take a leak
Unless you want someone else to take your seat.
What am I?
You appear to be
a ticket. Possibly a train or movie ticket.
They're only good once, it's common to have to stand in line to get one, there are many just like it but they are often barcoded or numbered and in any event only yours is yours, and if you leave your seat you may very well lose it.