I used to be required to track all the receipts for travel years ago, and at some point like a decade ago the state figured out way more money was being spent on budgeting, reimbursing, and auditing each purchase individually than they would save by just doing a flat per diem rate for food and incidental expenses based on travel location.

I still keep my receipts long enough to make sure I'm not going over what I will be reimbursed, but shred them when I get home.