Any data type can be stored session. Because it accepts all 
the objects

All types of data Which can be serialized can be stored in 
session and we can also store dataset in session

If you are using inproc then you can store any .net data 
type (non serializable also), but if you are using state 
server or sql server mode then you can only store 
serializable data types.

Sesions can store any type strings,objects, not values.

Eg:-Session["n"]=100//error(won't allow values directly
    Session["n"]="100" //correct
    String s=Session["n"].tostring();//reading Seesion values
    dataset ds=new dataset();
    ds=(dataset)session["n"].Tostring();