The Roaring '20s, known for its flapper women, zoot suits and jazz music, was also a time of Prohibition, or when alcohol was illegal, which subsequently gave rise to the mob and infamous gangsters like Al Capone. A speakeasy was a club during that period that illegally sold alcohol to patrons and generally required knowledge of a password for entry. You can re-create a speakeasy joint for a fun them at a party.
Procure a few old wooden crates and fill them with shredded paper. Place bottles of liquor, either empty or full depending on preference, within the crate and with their tops peaking out of the paper. Place the crates as desired around your event space.
Purchase gangster street signs from online party supply stores, such as those that simply read "Speakeasy" or those that say "Flapper Lounge," "Capone's Hideaway" or "Bathtub Gin Joint."
Drape feather boas around chairs and make centerpieces for tables using felt gangster hats, martini glasses filled with pearl necklaces and sequined flapper headbands.
Purchase a few life-size cardboard gangster and flapper cutouts to display around the event space. Look for cutouts that come minus the heads so guests can get behind the cutouts for picture fun.
Place foil music note balloons, which are available from online party stores, either separate or in clusters around the event space depending on preference.
Dim all lighting as a final touch to further set the mood of the party.
Hire a real jazz trio to play at the party if possible, or play '20s jazz music from assorted CDs or your iPod. Encourage guests to come dressed as gangsters and flappers, including wearing zoot suits. Purchase a plastic brick wall "scene setter" as another Roaring '20s touch for your party.