Dressing up like a gangster can be a fun activity for Halloween, but if you're not a real gangster you may not have the loot to afford a real zoot suit, or a real tommy gun. Cheap alternatives can help you to ham it up as a gangster without breaking the bank.
A wide brimmed fedora is de rigeur for any self-respecting gangster. Preferably it should be black with a white hatband. Look around charity shops and used clothing stores for cheap fedoras; if you're lucky you will find a gangsterish looking lid for not much dough.
Gangsters were supposedly fond of hiding their tommy guns and sawed off shotguns in violin cases. While you're at the charity shop, have a look around for a violin case to go with your fedora. Alternatively, borrow a case from a sympathetic violin-playing friend. Be sure to take the violin out before you go romping around on Halloween.
Double Breasted Suit
The double-breasted suit was the outfit of choice for 1920s mobsters. Many other people wore them as well, but they're remembered today as gangster garb. Because double breasted suits are distinctly out-of-fashion today, you may luck out and find one cheap at a yard sale, charity shop, or flea market. If you have older male relatives, ask them if they might have held onto one in the back of their closet. Compliment it with a black shirt and a white tie and you're headed toward gangsterhood.
"Moll" was a slang term for the female companion of a gangster, and it wasn't particularly complimentary. Coax a female friend to be your moll for the evening, otherwise the other gangsters definitely won't respect you. Ask your friend to find some fishnet stockings, a long cigarette holder, and a trashy looking dress. In addition, she should do up her hair in a 1920s style and wear garish makeup. Red high heeled shoes wouldn't hurt.
Two Tone Shoes
Finish off your gangster look with black and white saddle shoes. You can get old shoes pretty cheap at any thrift store, and convert them yourself using shoe polish or paint.