store dropdownlist into arraylist

Firstly, don't use an arraylist if you can avoid it - they aren't type safe so they are more work and less readable than they should be. Use a typesafe List<T> instead. That way you don't have to cast the array elements before you use them.

After that, it's pretty simple:
Declare your List<T> with the appropriate type (whatever you have loaded the DropDownList with)
Fill it using the the List.AddRange method, handing it the DropDownList.Items collection or the subset you require.

// Decalre 2 ArryList to Hold the Text and Value of Items
ArrayList alText= new ArrayList();
ArrayList alValue = new ArrayList();
//Copy the Text field in the First Arry List
foreach (ListItem li in objDDL.Items)
{
alTextt.Add(li.Text);
}

//Copy the value field in the Second Array List based on First ArrayList value
foreach (object item in alText)
{
string val = objDDL.Items.FindByText(item.ToString()).Value;
alValue.Add(val);
}

Code:

' - - - - - - - - - - - - - - - - - - - - - - - - - - -
' This will get info of certain list in an excel range
' The basis for look up is the cell one row above the first list entry
' (this cell is usually reserved for title of the first column)

Function xlrangeListCount(SheetName As String, RangeName As String, Optional OffsetC = 0) As Long
Dim thisCount As Long
With Sheets(SheetName).Range(RangeName)
thisCount = 0
Do
If Not (IsEmpty(.Offset(thisCount + 1, 0))) Then
thisCount = thisCount + 1
Else
Exit Do
End If
Loop
End With
xlrangeListCount = thisCount
End Function



Function xlrangeListItem(SheetName As String, RangeName As String, OffsetRow As Long, Optional OffsetCol = 0)
xlrangeListItem = Sheets(SheetName).Range(RangeName).Offset(OffsetRow, OffsetCol).Value
End Function


Now, here is an example of using those 2 function to create a dynamic array.

Code:

Sub GetRangeList()
Dim MyList()
Dim i As Long
Dim ListCount As Long

ListCount = xlrangeListCount("Sheet1", "A1")
ReDim MyList(1 To ListCount, 1 To 3)
For i = 1 To ListCount
MyList(i, 1) = xlrangeListItem("Sheet1", "A1", i)
MyList(i, 2) = xlrangeListItem("Sheet1", "A1", i, 1)
MyList(i, 3) = xlrangeListItem("Sheet1", "A1", i, 2)
Next

End Sub

Take note that this code assumes your list have headers(or titles) and the "A1" refered to is the first header in the list.

I assume you can put it (MyList()) in a combobox.