Stipulations:
- You cannot die and are immune to disease
- You cannot alter the future such that you change the world from your point of origin. i.e. You cannot become so famous that future people recognize you as immortal.
- If you vary the timeline too much you will cease to exist.
Would you bring some period specific cash with you on your trip?
That would be ridiculously expensive and time consuming. The question does not present a lead up scenario but one would assume whatever deal this is doesn’t allow for a lot of prep time or extra money.
Additionally any money that would exist in that time period that survived to today… would still be present in that time period. In a pre-computer world it’d be easier to get away with what is essentially counterfeiting or what would be explained as counterfeiting to those that caught you; but that’s still a massive risk for saving at best a few years building up that wealth yourself.
And that’s all assuming you didn’t create a paradox by allowing those two versions of the same item to exist simultaneously. Like you traveling back is fine, as you wouldn’t exist in 1945, but bringing items that did exist would either displace the money to avoid the paradox, changing the future possibly significantly which breaks the rules, creates a paradox which would cause you to no longer exist.
Why would we assume that? We assume that you become immortal, and are sent back in time, and the part that seems unrealistic to you is that you’d prepare for the trip before you go? :P
Any money that existed then would exist today, so you avoid anything serialized. Stick to things that are non-serialized and fungible- precious metals for example, or gemstones (without laser serial #s of course). Pre-serial cash would work too (probably the easiest to counterfeit in modern times).
But as for existence paradox-- the mere action of going back would create such an issue if it is an issue. All the molecules in your body and clothes existed in 1945, if perhaps in different arrangements-- IE anything plastic might have been in the ground as crude oil, the molecules of your body would be things like plants, dirt, trees, etc, anything metal you have would be ore in the ground, etc. And per butterfly effect paradox, from the instant you arrive you’ve changed things, just by breathing and walking around you’ve affected air flows and converted a little more oxygen to CO2. If you arrive in the middle of nowhere, hold still for 30 seconds, then depart again, that might have no real effect. Or it might create a butterfly effect that changes a weather pattern or something and has a huge effect.
By that measure, the whole thing becomes a not fun exercise in paranoia- knowing that even saying hello to someone (or not saying hello) might alter the future and erase your existence.