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The only thing you can do is rely on bank records to verify whatever expenditures you can. If you are missing bank statement/checks, you'll have to obtain them from the bank.
Also, for any large items you should be able to get duplicate receipts from the vendors.
Beyond that, you'll have to wait & see what the auditor wants. Many items, taxes, insurance, medical, securities transactions, etc., can be obtained from the party you did business with.