
That is a great choice for a collection theme! An important historic period with many interesting collectible objects, coins and banknotes just two examples.
Value wise, the French allied banknotes would be a few dollars at most, and I am guessing the same for the Italian banknotes. More than 100 million of each denomination were printed and they are not hard to find. I don't expect their value will increase much over the next few decades. The same goes for the German occupation banknotes. But I suggest you do not focus on their value or value increase, they are historical documents, each with its interesting background. If you are looking for good investments, there are better opportunities than coins and banknotes - they are high risk investments with possibly low or negative return.
Anyway, from a collector's point of view, WW2 Europe is certainly an interesting area and you have a good start with what you have there. Directions in which to extend your collection could be:
- The coins emitted by the occupied countries (as suggested by oriole). Like Germany, most countries switched from emitting coins in silver and copper to low value base metals like iron and zinc, and WW2 coins may have the same design as pre-war coins but be made in different materials.
- Local emergency money (such as in the form of low denomination paper money emitted by a town council). This existed to a certain extent, but not at all as extensively as during WW1.
- At least for France (my collection area, although mainly coins), there were special banknotes emitted by the Treasury towards the end of the war.
- Banknotes from the Allied occupation of Germany after the war. These were emitted at least by the United States and by the Soviet Union for use in the occupied zones and by France (the Treasury) for use in the occupied Saar region. There could be more, this is a bit outside of my focus area...
- Then there is all the exonumia related to WW2: bonds, postcards, posters, medals of course... depending on your preferences.
Good luck with your collection and, please, share what you find!