We usually leave $2-3 US, three if she does the dishes. We usually stay at the Palms, which does have a built in service charge (10%), so we feel this is above and beyond the service fee. At the end, we leave all kinds of left-overs, including bug spray to shampoo to change. Have generally left about $12-$15 in change in Bz.$. Last time, due to a bunch more folks, we left a lot of unopened food, and hope that someone was able to use it. By the way, you do have to tell them it's for them. They will not touch a dime left out, unless they know for a fact it's for them.