Meaning: Easily replaced or sacrificed:
* Disposable
* Sacrificial
* Consumable
* Throwaway
* Replaceable
* Dispensable
* Redundant
* Unnecessary
* Superfluous
Meaning: Not essential:
* Non-essential
* Marginal
* Trivial
* Insignificant
* Secondary
Meaning: Easily killed or destroyed:
* Vulnerable
* Futile
* Useless
* Worthless
The best synonym to use will depend on the specific context of your sentence.