HOW DO I PROVE MY EXPENSES
Keep all those tiny chits. It helps if you know how they were paid ie; visa, bank etc., It is not simply enough to have a bank or visa statement , you need the actual chit or bill . An auditor can ignore or charge back expenses without one. Often these chits fade so many people scan or photo copy them. In any audit each chit or bill you expense should have the vendors Name - HST number on it and description of the purchase. Otherwise the HST credit taken or the expense may get charged back. The auditor simply calculates the charge backs and with interest and penalty to the tax account.
So make sure when you interact you have the actual bill as well as interac payment slip.