Check out www.irs.gov. You can browse the pubs online without downloading. Keep in mind that if you suddenly showed a zillion dollars in 74.99 type deductions, you might not stay "under the radar" as Timebuilder recommended. But for most of us, the $75.00 rule helps. There is also a pub on recording for individuals but I think what you requested is covered in this section.
Publication 463, Travel, Entertainment, Gift, and Car Expenses, Chapter 5.
What Are Adequate Records?
You should keep the proof you need in an account book, diary, statement of expense, or similar record. You should also keep documentary evidence that, together with your record, will support each element of an expense.
Documentary evidence. You generally must have documentary evidence, such as receipts, canceled checks, or bills, to support your expenses.
Exception. Documentary evidence is not needed if any of the following conditions apply.
1. You have meals or lodging expenses while traveling away from home for which you account to your employer under an accountable plan, and you use a per diem allowance method that includes meals and/or lodging. (Accountable plans and per diem allowances are discussed in chapter 6.)
2. Your expense, other than lodging, is less than $75.
3. You have a transportation expense for which a receipt is not readily available.
Publication 463, Travel, Entertainment, Gift, and Car Expenses, Chapter 5.
What Are Adequate Records?
You should keep the proof you need in an account book, diary, statement of expense, or similar record. You should also keep documentary evidence that, together with your record, will support each element of an expense.
Documentary evidence. You generally must have documentary evidence, such as receipts, canceled checks, or bills, to support your expenses.
Exception. Documentary evidence is not needed if any of the following conditions apply.
1. You have meals or lodging expenses while traveling away from home for which you account to your employer under an accountable plan, and you use a per diem allowance method that includes meals and/or lodging. (Accountable plans and per diem allowances are discussed in chapter 6.)
2. Your expense, other than lodging, is less than $75.
3. You have a transportation expense for which a receipt is not readily available.