Consent case

So I'm trying to call which US Supreme Court case holds that a person must not specifically state yes to consent to a search. For example if they're asked if their bags can be searched, and they say whatever, this is consent. Could anybody refer me to the case I am looking for? It would be greatly appreciated!

The actual facts when consent is the issue are important. There is no case requiring a specific "yes" answer. You are doing legal research backwards. Without the facts, there is no issue. You go from the facts to the law (through case law) and not the reverse.

Give the facts and we can find the issue. If your issue is the person did not specifically say the term "yes" on the question of "can we search?" then you lose.

Like all fourth amendment issues, it is a totality of the circumstances. What are the circumstances?

Info edit:
For the determination of the basic question of what a reasonable person would understand from the exchange, see Florida v. Jimeno (1991) 500 U.S. 248.