Unless you know how to store them properly, not long. Dont know how long, but I would be really surprised if they last a few years.
Tobacco goes stale, is prone to damp and absorbs smells very quickly.
I assume this plan involves bulking buying cigarettes and in a few years standing on Moore St , with cigarettes under your jacket shouting at passers-by " Fags for sale". Forgive my cynicism, but it sounds like a dodgy way making a fortune. Also, as most people selling fags on the street have smuggled them into the country, you are risking arrest.
Have you asked any smokers would they buy cigarettes that had been under your bed for two years and how much they would be willing to pay for them ?
If I was buying cigarettes from any source other than an shop, I would expect a significant discount from the retail price.