It is always advisable to have documentation of any deduction that you claim on your income tax return, in case the IRS decides to take a closer look at it.
If you do not have your receipts, you may be able to document the purchase in another manner:
- credit card receipt or statement
- copy of the cancelled check
- if purchased online, you may be able to get a copy of the invoice from the vendor
This list is not all-inclusive - just a few ideas to get you started.
Even without a receipt (or alternative means of proving your puchase), you can still claim the expense. Please be aware, though, that the IRS may disallow it if they request proof and you cannot provide it.