I currently own a business and have a tax id #, etc. but I would like to start several other ventures aside from my original business. (Think: Coca Cola owning Lay's potato chips, and many other companies.)

Do I start theses business under a new tax id #? How does this work?

Ashley,

You should talk to your accountant and attorney about structuring it. In my case I have a company (LLC) that is 18yrs old. About 9 years ago we started another company, unrelated in product etc. from the first one. It was formed as an LLC also but the ownership (Member) is the first LLC. About 7 yrs ago we started a joint-venture with another company where products etc. were in common with the first. Again, it's an LLC with our interest held by our orginal LLC, and the other firms corporation holds their interest in it. The profits flow from each into the original LLC and are distributed from there.

While this may seem convoluted to some, there was reasoning behind it. First, it was a part of our exit plan. Any of the others can fail without harming the orginal business, and we can sell any or all of the businesses at any time without having to try and figure out how to separate them. Each has it's own business license, insurance, accounting etc.
Hope this helps.
Denny

If the product is related you can start it under the same LLC however if they are different then you will need to go with a new company altogether.

In my own business, everything is under one umbrella. That's because that the way I want to sell it.

However, all the products and services are geared to business owners.

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And I've seen some create individual businesses for each business.

I agree that the best person to talk to is a lawyer who has a specialty in business matters. A paid talk can save you lots of $$ and problems later.

In my business experience with multiple businesses, using a
d/b/a "doing business as" covers the 2nd company
under the same tax information that's owned by the first one.
For example using yours,
Coca Cola d/b/a Lay's potato chips would be covered under 1
umbrella, Coca Cola's.