Go to the IRS web site.
I am not an IRS agent however, reconstructed receipts may be acceptable to support your expenditures. It falls under the reasonability test (is what you reconstructed reasonable). Use photo copies of checks cashed, copies of credit cards expenditures, work invoices marked paid, etc. Credit card statements that specify places such as Lowe's, Home Depot, Kil-em-ded exterminator, etc are helpful.
DO NOT WAIT to see if you are audited. Start the work now and date your reconstructed receipts. Remember, the burden of proof is on you, not on the IRS.