Jim Cramer considered the rally on Wednesday to be a celebration of investors anticipating that the Federal Reserve will do nothing on Thursday—and it could be premature.

"Sometimes when I hear about this endless parlor game of will they raise or won't they, I feel like we have to step back and talk about what we're really about, our core DNA here on 'Mad Money,' which is evaluating companies as potential investments," the "Mad Money" host said.

Cramer wants investors who have saved for retirement and are ready to invest to look for opportunities to buy shares in companies at prices they like.

Thursday could be one of those opportunities.

Yet the "Mad Money" host finds that most investors only see two options with the ; buy if the Fed does nothing, sell if it raises.

Given the incredible run that the market has had going into the Fed meeting, Cramer thinks it could be possible that the averages get hammered if the Fed takes action. Yet, if it does nothing, the market could continue to rally and investors will regret that they didn't take action and buy high-quality companies when they had the chance.

"Less intrepid souls will most likely put money to work tomorrow after the meeting if they stay the low-rate course. Ultimately, I wouldn't be surprised if the traders who bought ahead don't boot stocks no matter what, just being glad they got some gains," Cramer said. (Tweet This)

That could be a fantastic buying opportunity.

More importantly, Cramer recommended having a fail-safe plan in place. After all, the Fed could surprise and decide to raise rates a quarter of a point and say it will take more action going forward. If that occurs, the gains from the past few days could be thrown out the window.

So here is Cramer's game plan:
If the Fed raises rates without a statement of reassurance that it is done raising rates, do not take the bait of the first sell. In fact, Cramer doesn't think he would even take action on Friday considering the amount of hot money that is betting that the Fed will not raise rates. Selling could be heavy.

If things get really ugly on Friday or Monday, Cramer wants investors to beware that various sectors will take a nosedive. Beware that they may continue to downslide with the market.

No. 1 Anything that's good for your body. That includes exercise, natural and organic. It includes Under Armour, Nike, White Wave and General Mills.

No. 2 Social, mobile, cloud and artificial intelligence. That means Salesforce, Google and Facebook.

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No. 3 Domestic retailers, as they are more immune to a strong dollar that will be caused by a rate hike. This includes Target, Panera and Kroger.

No. 4 Biotech will be creamed, as always. That could be a chance to pick up Cramer-faves Celgene and Regeneron.

"We need to stop fretting about a potential rate hike and start worrying about missing any opportunities that could be created by a Fed-induced selloff," Cramer said. (Tweet This)

Many investors fear the outcome on Thursday's Fed meeting. Yet, what they should be more afraid of is the fear of passing up an opportunity that may not come back for a very long time.

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