Buy a pizza and a coke on menulog and get $10 off your next order. A quick look shows places where you can get a pizza and coke for $11 (Brunswick Pizza Bar - $9 small meatlovers $2 can of coke). No coupon required so should stack with cashrewards too.
Nothing in the T&C says you can't use the $10 voucher to order another pizza and coke and get another voucher. However, the voucher is only good for delivered orders. Ensure you haven't opted out of marketing emails from Menulog or you won't get the voucher.
Excerpts from the T&C: "All eligible orders will receive an email the following business day containing their $10 Menulog voucher (…) Multiple entries are permitted. (…) Participating Outlet Means any pizza establishment listed on the Promotional Website that stocks any Participating Product (…) Participating Products means any Coca-Cola, Sprite, Fanta, Lift, Cascade, Kirks, Mt Franklin, Deep Spring, Zico, Glaceau Vitaminwater & Smartwater, Powerade, Barista Bros., Fuze Tea, Pump, Goulburn Valley, or Appletiser (…) the $10 Menulog Voucher referred to in the Method of Entry in the Schedule, is valid for seven (7) days from the date it is issued and can only be used for credit card and delivery orders only"
Most if not all places have a minimum order though. Most minimum orders start from around $20.