Had an item missing from my McDonald's order.

Contacted support, and they stated that per their policy, they would not refund the missing item.

Any firm whose terms and conditions state that they can fail to supply something you contracted them to provide, and that's "your problem mate", is probably a firm you should think seriously hard about ordering goods or services from.

Can't imagine any other type of good or service where a consumer would sign up to that agreement and forgoing their statutory rights.