For most expenses you need a receipt or similar document as evidence of your expenses. To claim a deduction for a work-related expense, as an employee:
you must have spent the money and you weren’t reimbursed
the expenses must directly relate to earning your income
you must have a record to prove it (usually a receipt).
You can only claim a deduction for the work-related portion of an expense. You can’t claim a deduction for any part of an expense that doesn’t directly relate to earning your income or that is private.
If your total claim for work-related expenses is more than $300, you must have written evidence to prove your claims.
If you are claiming the decline in value of a depreciating asset you have used for work, such as a laptop, you must keep records for 5 years following your final claim, including:
purchase receipts and a depreciation schedule
details of how you calculated your claim for decline in value