I'm wondering how the Romans would have said "yes" as in "yes please" or "no" as in "no thank you". I don't know if they would have said it exactly like that, but what would they have said if they had to mean something like that?
In Classical Latin, there were no words exactly corresponding to "yes" and "no". Non and ne were negatives, but they needed to combine with other words (like "not" in English).
There were, however, particles which could be used to agree with something. Both ita and sīc meant "thus", and became words for "yes" in the Romance languages. So if someone asked if you were lost, for example, you could respond "Ita!" ("It is so!"). For a stronger "yes", add vērō ("truly").
"No" on its own was a bit more unwieldy to express. Minimē is "not at all", minimē vērō even stronger. Negō means "I deny it!", nōlī is "don't!".
Another way to respond to a yes/no question is to repeat the verb, in the positive for "yes" and in the negative for "no". So if someone asked "are you lost?" you could say "I am" (sum) or "I'm not" (non sum).
At least in a few cases, I have been taught that Ita or ita vero is correct for yes. I have seen it used when answering questions. As @Draconis pointed out, Ita means it is so, and vero means truly or something like that. However, ita seems to be a shorter, more casual form, not different in strength. Another tactic I have seen (rarely) is to just reply with a verb. In English, this would look like: Do you speak Latin? I speak it. A standard form of no (at least for beginners) is minime.
The question has already been answered, but I cannot write this long stuff in a comment.
In the book: "Grammaire latine complète, mise au nombre des livres classiques par le Conseil Royal de l'Instruction Publique" by Émile Lefranc.
"In lieu of repeating the question, it's possible to:
-to express "yes", using the affirmative adverbs:
= all meaning "yes".
To express the negation, using negative adverbs:
-non Hercle vero
-nihil vero minus
-non ita est
= all meaning "no".
I will edit it if I find other ways, as listing them is very interesting.
I was surprised to find "non" to say "no", like in French, and not negating anything.
Probably a short familiar form.
I know this thread is about Classical Latin, but regarding Medieval Latin, in the 11th century Petrus Abaelardus (1079-1142) wrote a scholastic text entitled "Sic et Non".
From Wikipedia: "In Sic et Non, Abelard presents 158 questions that present a theological assertion and allows its negation." The first three questions are: 1) Must human faith be completed by reason, or not? 2) Does faith deal only with unseen things, or not? 3) Is there any knowledge of things unseen, or not?