Definitely take your camera with you, and have fun taking some wonderful photos! Guatemala is great for photographers. To add to the above comments:
1. Homeowners or tenants insurance often covers things like cameras when one is travelling. Check your policy, and if it is stolen, which it likely won't be, file a police report and get a copy for your insurance claim.
2. Never hand your camera to someone you don't know to take a picture of you.
3. Never take photos of children without first asking their parents. You can take great photos of people's backs, or a group, then crop as needed. Be sensitive to people who already may feel objectified as indigenous people. Respect a person's wishes if they say they don't want their photo taken.
4. I spend a lot of time in Guatemala. Sometimes I will ask a family if they would like a photo album of their family, something many people here simply could not afford. Then make sure to make the album and give it to them. There are lots of places to get photos printed in Antigua.
5. Bring enough cards -- you'll be taking a lot of photos!
6. Back up your photos of flash drives in case something happens with your camera. The camera is replaceable, the shots aren't.
7. Don't forget the battery charger and an extra battery.
8. Also the cable to download photos, if you will have access to a computer to transfer your shots to a flash drive. Otherwise, just bring extra cards and store the full ones somewhere other than with your camera.
9. Antigua is generally fairly safe. But, in addition to the above advice, don't carry your camera around in plain site at night if you are alone. Rather than carrying a camera case, I use a foam and Velcro wrap available in most camera stores, and put my camera in my backpack -- below other stuff if I'm not going to need ready access to it.
Enjoy your trip! You just might fall in love with Guatemala, as I have!
Eliza