What are your favorite accounting / financial hacks for startups?

Are there any unique tips and tricks that you use in your startup when it comes to credit cards, expenses, etc?

My favorite hack: getting an American Express Centurion Card (Black Card) by using payroll.

While spending $250,000 a year (minimum needed to be invited) on yourself is out of the ballpark, it's fairly easy if you have paid full time employees.

Sign up for a payroll provider like Trinet and put the expenses on any existing american express card that you have. i.e. Instead of paying for Trinet directly via ACH, charge it to an Amex card first, then pay it off.

Once you reach $250,000 spent on payroll and other expenses within a year, you'll get invited to become a Centurion Card member.

There are many benefits of the black card, including free upgrades to business class when you buy economy tickets.