Well, this question could be vague. For Halloween, you can choose anything to dress up. However, typically stuff that scares people would be better.
i do not no!!
you can just get an tuxedo and maybe a red bow tie and some black or white shoes
www.buycostumes.com has cupcake costumes to pick from. www.coolest-homemade-costumes.com/homemade-halloween-costume.html also has ideas, pictures, and instructions on how to make a cupcake costume.
There is no commercially available Whopper Jr. costume from the Burger King commercial, but you can find some homemade versions on Ebay.
Cause play websites
If you are looking for more information on what are some suggestions for cheap Halloween costumes for my son, the best place to look is on freefrombroke.com/before-you-buy-that-halloween-costume
They can try building their own Lego designs. They can also try making homemade decorations!
Blues brothers is a good one, easy and recognisable, also straight :)
The most popular Halloween costume for medieval times is a knight. You can find out how to make a homemade knight costume here: www.coolest-homemade-costumes.com or buy one here www.buycostumes.com
dress up as an evil rabbit.
There are many peacock costume ideas for children. peacockcostume.com/ and www.coolest-homemade-costumes.com or www.ebay.com/sch/i.html?_nkw=peacock+costume
Just wear nothing and put on a mask.