This is hilarious man. Just read basic OPT guidelines before asking here in sajha.
As for your question, here are the answers;
Why don't you "manage business" of a chinese buffet by working as a waiter if you are "business major"
or program their billing computer if you are "software engineer"
or inspect food hygiene, if you majored in food science or even toxicology
or maintain heating and cooling systems - engineer
A cart business is something like things stated above. However, you DEFINITELY can start a business during OPT, not a cart business. I can understand how hard to find a job, but please don't waste your time in such crazy ideas. Good luck!