If your contract stipulates 21 consecutive days leave; does it include public holidays and weekends; or is it actual 21 working days?

In a contract case, the language of the contract controls, so look first to anything in the contract which would help establish this--that includes any express or implied definitions of "days" or "workdays" found elsewhere. Look also to how other types of time off might be handled--is there any guidance from what happens if vacation days are used together with holidays or weekends? Look also to practice at the work place to help define how it's done: what's happened with other employees with similar terms? Finally, look to other contracts in the company; if other employment contracts (or the employee handlbook) define it one way or another, that suggests it should be defined that way here, too.

Ultimately, there is no absolute right or wrong answer: a contract could legally be 21 consecutive working days, as extended by holidays and weekends; or it could be 21 consecutive calendar days, including holidays and weekends. If there literally is no guidance on the subject, you can certainly argue whichever better fits your position, but if the other party disagrees, you'll end up either having to settle/negotiate/compromise or even potentially litigating if the disagreement gets that heated.