The Gospel is more valuable than money, but it cost you ten cents or less to buy that tract. What did the tract give to the person who is wondering how they are going to feed their child on a salary that is much less than minimum wage when no one tips them real money? It gives them the feeling that Christians are cheapskates and selfish. Some may even get the impression that Christ is as fake as the money that you tipped them with. That is not the right impression to give someone that you want to become a Christian.
Giving them a tract is great, giving them fake money is not. Please consider that most waiters and waitresses are barely scraping by. Give them a real tip! When they have some of their bills paid, and their kids are fed, they are much more likely to respond positively to a tract.
Source: Waiter Gets Fake $20 Tip, Turns Out To Be Christian Pamphlet