Is it ok to show up to a conference without registering if I don't eat any meals?
No, it is not acceptable.

You can of course email the organisers and ask if you can participate without paying, but do not be surprised if they say no.

(Please note that conference registration fees cover lots of things besides the lunch. Among others, conference registration fees may cover the rent of the hall in which you are sitting, and expenses related to the speaker who is giving the talk. Conference organisers are definitely not expecting random people to come there without registering, unless they explicitly advertise this possibility.)