If you're male, go naked wearing roller skates, and be a pull toy. If you're female, go naked except for tall boots, and be Puss in Boots.

Seriously, type "Halloween costume ideas" or some such into a search engine--there are sites that have lists of costume suggestions.

One year I went as a tombstone. It was a bit bulky, but it uses one simple prop--a cardboard box painted gray, with armholes and a headhole. I wore black and painted a smart aleck epitaph on it (the possibilities are endless there). At this particular party, I was trying to be unrecognizable to friends, so my head was covered by a black T-shirt poking out of the top of the box. I didn't even punch eyeholes in it, but could still see through the fabric. Easier for talking and drinking would be a black hood and eye mask.

The basic ghost using a white sheet with eyeholes is pretty easy, and although it's a cliche hardly anyone does it, so it may be unique at your party.

A 50's/60's nerd isn't too difficult. For a male, too short pants, pocket protector, plastic frame glasses with the bridge "repaired" with thick tape, maybe a bit of toilet paper stuck to the bottom of a shoe. For a female, catseye glasses, clumsy makeup, prim hairdo, unfashionable skirt and blouse, dark lace-up shoes with dark socks. (Skip this idea if this is how you usually look.)

An old man/woman can be done with an old person mask, white wig or baby powder in the hair, cane, and appropriate posture and speech. (Skip this one if you actually are old.)

One year, in an attempt to be unrecognized in costume, I planted a red herring by showing up in regular clothes, acting pitiful and saying I couldn't think of a costume. After establishing my presence, I snuck into the bathroom and put on my white sheet. I hunkered down to disguise my height and danced with people of the same sex. It worked.

Whatever you do, have fun!