On our first and last trip to Cancun (all inclusive), we tipped at breakfast and dinner, we didn't really know if we were suppose to or not, but we left 2-3 dollars. We didn't really even think about the maid service, we don't get out much.
I do not, but then I do not utilize the maid services; I place the do not disturb sign up during my stay. Seriously, they give me enough towels for 3 weeks! That and I habitually straighten a hotel bed before I leave the room in the morning. I have my own toiletries, so the others sit unopened and undisturbed on the counter. I do not use the coffee makers or anything either. I am likely the most unobtrusive guest a hotel ever sees.
I also cart my on luggage (1 carry-on suitcase will work 5 days/4 nights for me), so no tip there.
I will tip for the free breakfast though, if it is type of place that offers table service (i.e. fills your coffee, etc...) or makes omelets to order.
We left them some beer in the fridge.