The easiest way would be to collect the entire list into an array, and then build the string that is shown by the messagebox.
Something like this:
Dim arrItems : str = """" : count = 0
arrItems = array(""Item1"",""Item2"",""Item3"",""Item4"",""Item5"")
For Each x In arrItems
str = str & x & vbTab
If count Mod 2 Then str = str & vbCrLf
count = count + 1
Next
Msgbox str