So, you are reading this because you either need a costume for Halloween or a convention. And, obviously you waited until last minute. It's okay, don't freak out. Breathe in and out. I have 6 suggestions to help you cleverly come up with a easy costume for your upcoming event.
1) Any cast member of Bob's Burgers.
They all wear basic clothing, you would really only have to worry about certain accessories for some of them like glasses or Louise's amazing hat. You can find most of these items at stores, though. And, you may even have some of the clothing items already.
2) Any cast member of Adventure Time
So many of the characters in Adventure Time have costumes based in regular clothing. Well...the main characters anyway. Raid your closets friends! I'm willing to bet most of you have a blue t-shirt. If your favorite character is something a little more intricate like LSP try finding a purple dress and wig. Draw a pretty star on your forehead and slay like she would.
3) Mario and Luigi
Guys, really, all you need are some overalls and a red or green long sleeved shirt. You can buy the Mario and Luigi hats on for a fair price. If you're more crafty you can buy a hat and make the M or L out of white craft foam. Super easy and fun.
4) Resident Evil Characters
I realize that some characters are harder than others. Nemesis would be crazy hard, but Jill, Claire, Leon, and most of the main characters have clothing that's easy to piece together. Hit up amazon or an army surplus store for tactical gear. If you have a few days before your event I made tutorials on how to make a Claire Redfield cosplay.
5) The Queen of Halloween - Wednesday Addams
If you have a dress with a peter pan collar you're set. If you have long black hair, you're even more set. To make this even more simple most stores sell peter pan collar necklaces for under $15. If you already have a black or dark colored dress you're all set. This is easily one of the cheapest and most recognizable costumes you could do.
6) Homicidal Maniac
Maybe you just weren't digging any of my ideas, or maybe you just don't have time. You could always quote Wednesday Addams. She speaks the truth. You could also check out Rachel Zimmaro's 11 Last-Minute Halloween Costumes for more ideas.