I’m no gemorah scholar but I happen to know there is one that states that if you are travelingto yerushayim for the shelosh regalim, and you are put up in a local residence for the chag, when you leave, you should give the head of the house animal hides as a token of your appreciation.
I know this because when I used to work in a Jewish establishment, this was hanging up on the wall where the workers could see, and quote, to show that it is the right thing to do and very much a jewish concept to tip.
At the end of the day regardless of what you are already spending, or how much you make, you ordered in for a reason, and that’s because you either could not or did not want to go outside and pick it up yourself, so there is a person performing a service on your behalf, the least you can do is spare a dollar or two , no one’s asking you to pay his salary.
It also seems that in life, if you are not generous to others, who will be for you? Its really just a few dollars, probably the same as your morning/afternoon coffee, yet for someone else its a chunk of their earnings, I think its time for a little perspective.