Just an FYI, I only have a modest interest in Roman coins, so I'm nowhere near a specialist. These are taken from some notes I've picked up over the years, which I hope might be of some use to you.
On the obverse, I agree that it is IMP Gallienus. Not sure if its PF or PP, but I think PF is more appropriate, then AVGG. Any further text is lost to my eyes.
So that's coin shorthand for “Imperator Gallienus, Pius Felix Co-Augustus”.
“Emperor Gallienus, The Pius and Fortunate Co-Emperor”
It might seem a bit weird to have two emperors, but apparently he did reign with his Father from 253 to 260, before ruling alone until 268. That's what the extra G is for in AVGG. If it was a single G, that's just Augustus instead of co-augustus.
That's also why I discounted PP, as that's Pater Patraie “Father of the country”, which I'd have expected to see on a coin featuring the elder ruler rather than the younger ruler in a co-emperorship.
Ancient Rome had two words we would translate to emperor today, although that's not perhaps truly reflective.
Imperator is roughly equivalent to “Conqueror” - as I understand it, any successful battlefield commander could be declared an Imperator, the emperor got to put it on coins as a position we might better understand today as “Commander-in-Chief”.
Augustus was the first actual emperor (Julius Caesar was his adoptive father, but he himself only ever was “Dictator for Life”). Anyway, many subsequent emperors claimed some line of succession from Augustus, which “legitimised” their right to rule. By putting it on the coin, they're claiming to the world this “legitimate right to rule”.
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Reverse
Annona was the goddess personification on grain, and many emperors did give out free (or highly subsidised) grain in Rome - largely for popularity with the people. Plus the image does look like someone holding grain. That's probably correct.
Many emperors did put AVG on this side too, to remind people of the link between them and this Goddess. I think I can pick some of those letters out.
The 3-4 O'clock position in the green is probably SC “Senatus Consultum”, “By decree of the Senate” - To become emperor still required recognition by the Senate, so that's another piece of “legitimisation”.
I don't believe there's anything in the grey area, beyond age damage which might look like symbols, and I can't quite pick out anything in the start of the green section.
But what we have is “ANNONA AVG ??? SC”.
I would roughly translate that as “The Giver of Grain, The Emperor ???, as approved by the Senate”.
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I do hope that was of some help to you, and perhaps brought you some of the knowledge you were after. As I say, amateur here so I could be wrong. And as this is the Internet, I'm sure someone will be along to correct me any minute! 😛