We usually put 5-10 dollars in cash in each envelope and tell all of the CM's (Server, Room Attendant, etc) to have a few drinks at the bar on us.
One tried to give it back when she said she didn't drink. I told her to use it on something that would bring a smile to her face. I find these little things often mean a lot to them.
Room Service we usually tip 3 bucks per order, larger if its more items of course but usually we order about 5 things each time.