I don't own this book, but this is the exact map that we used.
You'll definitely want a book on Angkor to carry around. My sister had a great one and I'll get the name of it when she wakes up - dumb time difference. I think the most important feature would be a good map, descriptions of all temples within Angkor, and some "iconic" photos because they're fun to replicate.
A nice pair of walking shoes is important, too. I do not... I repeat, DO NOT... recommend Shape-ups. I just think that they're hilarious and, up to this point, I may have led you to believe that you needed them. As I said before, I lived for my Crocs on this trip. It wasn't just because they were comfy (that was huge), but they also washed off easily. Trust me, after walking around for about 30 seconds our shoes were covered in red dust. There's no doubt in my mind that my tennis shoes would have been ruined had I worn them the whole time.
Having a nice, light scarf or shawl with you is important. It was way too hot for us to wear sleeves, but some parts of the temple will require your shoulders to be covered (Some even require your knees to be covered - keep that in mind). We didn't use our scarves once because when we had the opportunity the section of the temple was closed. Bring it. If you don't, you'll need it.
Drinking water. Don't get me wrong, there are places to get bottled water everywhere. I just want to stress that you can't drink the water in Siem Reap (or any part of Cambodia). My sister carried around a CamelBak water bottle, like this one, and it worked out pretty well. Although, there were a few instances that it got sand on the rubber nozzle. Looking back, I would have carried around a collapsible water bottle so that I could store it away when it was empty or we were traveling.
Two things: Spicy food and those times when you accidentally drink the water. Enough said.
Malaria is an issue in parts of Cambodia, one being Siem Reap. Bring something strong to keep the "sceeters" away and you'll be fine. Well, I think it takes around 2 months to show signs... so ask me next month. Ha! Just kidding, but seriously... ask me in a month. If you want to know more information, you can check the CDC website. Also, if you consider taking medication prior to going or during your stay, really research it. My sister and I opted to not take anything because of the severe side effects.
Purell is nice anywhere! I had some attached to my backpack and I used it often. We were getting relatively dirty so it was nice to feel like my hands were clean.
In my opinion, bringing a day pack is absolutely necessary. We both carried our bags around with us everywhere. Tabitha chose something similar to the Osprey Flapjack Courier Bag and I had the pack that zipped off my Osprey Farpoint 55. They were great! Actually, I was super surprised about how much stuff Tab could fit in her bag. It looked so small, but I swear it was like magic.
Be sure to have a camera, particularly a nice one. We are both lucky enough to own DSLRs (I have the Canon t2i and she has the t3i) even though we don't know how to use them. We learned a lot over the course of our time in Siem Reap and, seriously, what better place to learn how to use a camera!!?? Also, try to have 2 different lenses. We always had a nice zoom lens on one camera and a 55mm on the other. It made for a great variety of photos!
Lastly, have a great travel buddy. Traveling alone is great - I do it a lot - but it's definitely nice to be able to experience Angkor with someone else. It's a beautiful place that has no words that truly describe it. Having someone with you will let you know that it wasn't all a part of your vivid imagination! They also come in handy for a good laugh. I will leave you with one instance of just that:
We were at Angkor Wat hoping for a beautiful sunrise. It didn't happen, but that was fine. We were just going to head to the pond to get an awesome picture with the reflection of the temple in the water. On our way to the pond, the conversation went something like this...
T: Ah, man. I bet we can't get a good photo since the sun isn't out.
K: I'm sure it'll be fine. It just won't have a blue sky.
T: ... but the sun isn't out. We won't be able to see it.
K: Yeah we will. Just not the actual sun.
T: ... no, but we won't get the reflection.
K: Ummm, what?
T: We need the sun for the reflection!
K: Omg! Tab, it's not a shadow!