Coding a Button to display a list of items in a ListBox

I'm having tremendous trouble in coding a Button that will display items, that I have selected in a program, in a ListBox.

Public Class Form1
    Private Sub btnCalculate_Click(sender As Object, e As EventArgs) Handles btnCalculate.Click
        If rdoNormal.Checked = True Then
            txtTotal.Text = 1.05
        ElseIf rdoThicc.Checked = True Then
            txtTotal.Text = 1.05
        ElseIf rdoCrusty.Checked = True Then
            txtTotal.Text = 1.05
        ElseIf rdoCob.Checked = True Then
            txtTotal.Text = 1.05
        End If

        If rdoSausage.Checked = True Then
            txtTotal.Text = Val(txtTotal.Text) + 1.8
        ElseIf rdoTurkey.Checked = True Then
            txtTotal.Text = Val(txtTotal.Text) + 3.25
        ElseIf rdoCheese.Checked = True Then
            txtTotal.Text = Val(txtTotal.Text) + 2.4
        ElseIf rdoPopchick.Checked = True Then
            txtTotal.Text = Val(txtTotal.Text) + 0.84
        End If

        If chkMayo.Checked = True Then
            txtTotal.Text = Val(txtTotal.Text) + 0.6
        End If

        If chkButter.Checked = True Then
            txtTotal.Text = Val(txtTotal.Text) + 0.6
        End If
    End Sub

    Private Sub btnReset_Click(sender As Object, e As EventArgs) Handles btnReset.Click
        lstReceipt.Items.Clear()
    End Sub

    Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
        Application.Exit()
    End Sub

    Private Sub btnReceipt_Click(sender As Object, e As EventArgs) Handles btnReceipt.Click
       **(What do I put here?)**
    End Sub
End Class