At your discretion you might also consider tipping your Tour Leader in appreciation of the efficiency and service you receive.
Although entirely voluntary, tipping is a recognised part of life in this region of the world. Some local staff will look to members of the group for personal recognition of particular services provided. Accordingly, you should allow US$ 40 for tipping of local drivers, guides, boat crew and for any miscellaneous tipping of hotel staff.
In order to make things easier for you, the Tour Leaders may organise a group's tips kitty and if this is the case, they will account for it throughout the tour.