I know one of the professional bars (the long tables where the mixologists work, not the buildings themselves) has the option for customers to buy food.

I placed several of the bars in my Showtime neighborhood cause the bars that come with that pack don't include the full-service bars with mixologists. They are just self-serve juice bars with no food options.

So I wanted food in my clubs and that's about the only way, except after I'd gone thru Edit Town and put in the bars I went to try them out and I couldn't get any food.

I must have put in the wrong bars obviously but which one do I want?

Either the prof. Dive bar or the smart prof. bar, but I think it is the 'zoning' for the lot that makes food available.
Dive bar etc will def have food, maybe Hangout will too, but I don't think so. I'm pretty sure it has to be one of the LN venue zoning. Changing the zoning shouldn't 'interfere' with the other uses for the venue imo. Why not try it. Another option, altho not ideal, is in bld mode, click on com objects, misc, and you will find the com. picnic table. Wherever you place those, you'll no longer have hungry Sims, they just unpack their picnic baskets!lol, even had a visiting performer sit down at the picnic, then leave when he's 'programming' stepped in!

The food available depends on the location. Based on my work in Bridgeport, most lots wont have any food. The nine clubs types plus the gym will have food as long as there is a bar there.