Always drink boiled or bottled water, never from the bathroom faucets. The heat of Chisec and Petén might cause dehydration, be sure to drink sufficient liquids. Always take with you a first aid kit, especially if you suffer from a specific illness. Always take with you mosquito repellent. If you can, take lots of vitamin B before and during your trip, mosquitoes hate it and won't come near you. Bring a pair of sandals or flip flops for the showers. It is custom in Guatemala to throw toilet paper in a wastebasket, not in the toilets because they are easily tapped. It is also useful to carry your own stash of toilet paper everywhere you go.