While we are talking about tips i just wanna say that the 15-20% thing is totally ludicrous, yeah it works sometimes when you sometimes have the average amount of food ordered, but if you order 100 in food for two peopel you dont owe the guy 20 bucks.
I deliver chinese food, and make ok money but if somebody orders 100 bucks i dont expect or get 20 bucks for a tip, or if somebody orders 10 dollars a 1 to 2 dollars tip often isnt enough to compensate for burning half a gallon of gas yet alone the cost of owning your car and if you want extra money in your pocket for the effort its just not happeneing. The 20% rule is garbage and i think tips should be made soely on what has been done.
For a delivery driver 1.00 per mile distance +1.00 is a good method. As a cheap car cost 34cents per mile to operate and the deliver driver does have to go both ways, so it cost him 68 cents per mile total, adding one dollar for his time, this in combination with the extra 32 cents per mile will compensate for more time driving and ensure that the driver makes decent hourly wage.
For waitors i use 20-30$/hour divided by the number of tables they are working multiplied by the fraction of an hour i sat and demanded there attention.
In casinos i tip someimes but i limit myself to 3-4$ per hour tips and put them in as bets at really high counts to make an extra effort at making the dealers more money. If everybody did that, they would make money