Using Checkbox From The Calendar Control - Able To Access The Values

I am implementing a leave system using the calender control. Something like below :- Following is the markup :-

<asp:Calendar ID="Calendar1" runat="server" ondayrender="Calendar1_DayRender"
ShowGridLines="True">
</asp:Calendar>
<asp:DropDownList ID="DropDownList1" runat="server">
<asp:ListItem Value="vacation" Text="Vacation" />
<asp:ListItem Value="sick" Text="Sick" />
<asp:ListItem Value="training" Text="Training" />
</asp:DropDownList>
<asp:Button ID="Button1" runat="server" Text="Save" onclick="Button1_Click" />
Following is the code-behind :-
protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)
{
if (!e.Day.IsOtherMonth && !e.Day.IsWeekend)
{
CheckBoxList list = new CheckBoxList();
list.Items.Add(new ListItem("Half day"));
list.Items.Add(new ListItem("Full day"));
e.Cell.Controls.Add(list);
}
}

However, I am not able to access the the checkbox values neither in the button_click event nor in the DayRender event? Is there a better way to implement this?