A gangster theme party idea can be as elaborate and realistic as you want it to be. Of course, without the danger. Although the modern gangster can sometimes be portrayed as glamorous, the 1920s and '30s was arguably the golden age for gangsters. Back then, gangsters disguised danger with the clean-cut class of zoot suits and fedoras.
So, you've chosen a gangster theme. Even when you choose a gangster theme, there are various sub themes from which to choose. A few ideas of gangster theme ideas include a speakeasy bar, Bonnie & Clyde, Al Capone, a Clue-style murder mystery, Chicago, 1920s Harlem or Little Italy.
Do justice to the era. Send an Art Deco inspired invitation using 1920s and '30s slang. Remember, this was the time of prohibition, when alcohol was illegal, but secretly served at speakeasies. You can include an illegal admission to a speakeasy with a cryptic password on the invitation. State the dress code, so that everyone shows up according to theme. For example, you may want to include a photo of a gangster and/or flapper seamlessly into the design of your invitation.
Require men to show up as 1920 and '30's gangsters. Provide women with the option to show up as gangsters or flappers. You may even want to go as far as recommending wardrobe ideas within the invitation. Flappers can dress up in flapper dresses, long pearl necklaces, boas, filtered cigarettes and fans. Gangsters can wear zoot suits, white tops with suspenders, fedoras, cigars, and fake guns.
Keep the vintage look consistent both outside and inside the party. Find a place to hold your event. Consider cocktail bars, ballrooms, or even your home depending on the size and scope of the party. Decorate with black & white tableware, wine bottles on each table, tons of candles, wrought iron wine holders and candle holders. Depending on the appropriate nature of the event and age group, you can also transform the location into a speakeasy back room with alcohol and gambling. Find recipes that existed during the times, like Mint Juleps and Champagne Punch.
Candles certainly help with mood lighting. Another idea in creating a speakeasy is low lighting and atmospheric smoke with a fog machine. You can even hire a DJ or a band to play rag time or jazz. Get a dance floor. If your party is elaborate, hire a group of costumed dancers. Invite a dance instructor who is an expert of the Charleston, Peabody, Fox Trot or other partnership dances of the time.