This is the hardest thing... As a designer, you have to save receipts for everything you buy for a show and then turn them in to be reimbursed!
I know this doesn't sound that hard - BIZ 101 - but it's surprisingly hard to follow through on. You forget to label the receipt immediately because you're grappling with cards or cash, wallet, purchase, there's someone waiting on you and so on. You lose or mis-file the receipt. You're so darn busy finishing the show that you put off organizing receipts. Time passes... A year later, as you do your taxes, you realize that you forgot to ask for repayment and that all those forgot-to-asks add up to a tidy sum. Maybe a car payment.
So today I'm herding a sliding mess of tiny, slippery receipt slips across my desk, trying to catch up. Yuck.