Create another company, create division under existing or just do all activity in existing company?

I have an s corp whose irs tax code is a specific business activity. I'd like to start adding two or three other activities that have nothing to do with the existing business activity in any way. My question is, should I:

 

1. Create completely separate companies for each activity

2. Create divisions under the existing company

3. Just do all activity in existing company and not worry that much about it?

 

Basically, does branching out into activities outside of your tax code create the need to start new companies, or is there a tax code that is very general, like "holding company" or something like that?

 

Thanks in advance!