Just add to the cart/checkout, no payment info needed. Although they ask for your email so you'll probably get updates from them trying to sell you products.
But you can only get 1 per order and I just realized it's flake food..
They're not flakes, they're crisps. It does not matter how many you order, they will send one. I have not gotten any spam from them yet. Maybe one or two emails in the 3 or 4 months since I've received them.