Should I let my son see smoking and drinking at home?
Probably not. Why do you want your son to see smoking and drinking?
He's old enough, he should learn to decide what's good for himself.
Even if your son is old enough, you shouldn't normalize smoking and drinking. Your son can make his choice on what he wants to do but you don't need to influence him to do it.
I got nothing else to do, I can't help it wanting to drink and smoke.
It seems you are having a problem if you cannot stop yourself from drinking and smoking. There are many things to do that don't require you to drink and smoke in front of your son.