$100 a day for food, $250 US lodging ($350 for NY, Chicago, LA), $400 Europe, $500 Asia, allow room service and movie, no overtime for salaried employees, let them book their own flights– they know their schedules best, allow business class on overseas flights, buy them lounge access for a year (their choice).
It's not worth nickel and diming employees, they will just turn on you.
If you're a service business with billable hours, inform your clients of your policies and bill it through to them,