If 'etc.' does not end a sentence, should you use a comma - i.e. "The room was full of party decorations, including strippers, bongs, etc., and machine guns.
You might use a comma after an "et cetera" in mid sentence. However, since in your sentence you are already using the open-ended word "includes", the "etc." is unnecessary.
I will also point out that most people would not think of strippers, bongs, or machine guns as "party decorations"!!