I got faced with the same question when I tried to translate the following phrase from Afrikaans into English:
"Ja nee wat, dit was darm lekker ou dae daardie."
"Yes no what, it was though nice old days that". (word by word translation)
In Afrikaans, "ja nee", " ja nê" and "nee wat" are all possible interjections to express nostalgia (but can also be used in many other contexts), and in my example above, stands completely separate from the actual words expressing a longing to the dreamy good old days of the distant past.
My best suggestions for expressing nostalgia (in the context of the above) would be a sighful: "Yeah" or "Ah"
Closest translation that still carries the sentiment:
After Jacob recounted some wild childhood adventures they had and all thing things they got away with, Pat nostalgically replied "Yeah! You are right! No, I agree! Those were the good old days!"