Anything that you claim as an expense to the business or as a deduction on your tax return is eligible to be asked about during an audit. Although the chances of audit are not high, you will have much more confidence in the event of an audit if you are prepared. Keep receipts for everything. Using a credit card is okay, but it is not enough in some cases.
Where services are rendered, an invoice describing them may be required. Special attention should be given to any item that is a material amount of your expense for the year or which has special use, like sports tickets or business development expenditures. In today’s electronic age, there is really no reason to get rid of receipts. That said, three years after the filing of the return or seven total years should cover almost any situation.