I know some Russian- will I be able to understand Bulgarian when I travel to Bulgaria?

I have heard that the two langauges are fairly similar and have listened to some basic Bulgarian in the past and understood it fairly well. Was it a fluke or is that a common experience? Also, if I speak in Russian, would a Bulgarian speaker understand (and not be offended?)?

Ye, probably a lot of it. Im a Russian speaker, and every time i hear either Bulgarian, Yugoslavian, or Chech, or Polish i understand alot of it especially Bulgarian and Polish.

You should be able to understand a lot of what is spoken in Bulgarian if you listen well. Although, remember to allow for the language not having word cases (padezhy) as Russian does. Also, Bugarian uses articles, equivalents of English "a" or "the", whereas Russian does not.
As for offending Bulgarians when trying to speak Russian to them, I understand that should not be a problem in general. Bulgarians and the Serbs are the most pro-Russian of the Slavic nations.

You will be able to decipher the overall meaning, but won't understand every single thing. It really depends on how well you know Russian too. When I hear Bulgarian a lot of it sounds like old Russian to me. For me, I would say it's the most understandable Slavic language after Ukrainian and Belarussian. All the Bulgarians I've met have been very friendly and they don't claim that Russia occupied them. Of course, it's always best to know the official language of the country you're visiting, but I think you'll be able to get by with Russian. Do try to learn some common Bulgarian words and phrases.

Yes, you will be able to understand *some*. Even though the languages are from the same group and sound similar, they are significantly different. If you read Cyrillic, you may have easier time, too. People would not be offended if you spoke Russian to them, if anything they would be amused and appreciative of your efforts. People over 30 studied Russian in school for years, the younger generation switched to English.

These days, most of the people you’ll meet at touristy places around the country speak at least *some* English. Restaurants often have menus in English, front desk staff has language training, museums, monuments and other places of interest have brochures in English – some translated better than others :-)… In general, Bulgaria is a very tourist-friendly and hospitable country.

Oh, on the body language part, make sure to note that Bulgarians shake their head sideways for a “yes” and nod for a “no” – may be veeery confusing to you at first!