Alternative to a "label" to carry around variable values?

Normally, when I have to carry around a value on a webpage while the user is busy clicking buttons and all, I store important values (such as an ID number) in a label control.  This way, I can always access the value of that label at any time.  I'm assuming that's not the correct way to store data like this however.  What's the correct way?

For example, if I wanted to store an ID number, I'd normally do the following:

<asp:Label id="lblID" runat="server" visible="false" />

<asp:Button id="btnSubmit" runat="server" onClick="btnSubmit_Click" />
protected void Page_Load(object ...